Cryogenic Methane-Air Separation Using Feed-Derived Nitrogen Dilution
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Solution Overview
Problem
Current cryogenic separation processes for methane enrichment from gas streams containing methane, carbon dioxide, nitrogen, and oxygen face challenges such as the formation of explosive gas mixtures due to oxygen concentration, high operating costs from external nitrogen use, and inefficient methane recovery, particularly in biomethane production from nonhazardous waste storage facilities.
Innovation Solution
A cryogenic separation process where the dilution stream consists of nitrogen extracted from the feed stream, rather than an external source, is used to dilute oxygen in the distillation column, avoiding explosive mixtures and reducing nitrogen consumption. This process involves cooling, decompressing, and separating the feed stream to inject the nitrogen-rich gas phase into the distillation column, while using the liquid phase to prevent methane loss and optimize separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If external nitrogen is used to dilute oxygen in the distillation column, then oxygen concentration is reduced below explosive limits, but operating costs increase due to nitrogen consumption
Solution Approach 1:
The system uses itself to provide the dilution function by extracting nitrogen from the feed stream and using it to dilute oxygen in the distillation column, eliminating the need for external nitrogen supply
Solution Approach 2:
The feed stream serves multiple functions: it is both the material to be processed and the source of dilution nitrogen, allowing one stream to perform multiple roles in the process
2Object-affected harmful factors
If pressure modulated adsorption with selective adsorbents is used to remove nitrogen and oxygen, then oxygen and nitrogen concentration is reduced, but methane recovery rate decreases making the process economically uninteresting
Solution Approach 1:
The harmful oxygen component is extracted and removed from the system through the distillation column, while the nitrogen is retained and reused as dilution gas, separating the removal function from the dilution function
Solution Approach 2:
The process changes the concentration parameters of oxygen and nitrogen through distillation rather than using adsorption, achieving impurity removal while maintaining methane recovery efficiency
3Manufacturing precision
If cryogenic distillation is used to separate methane from air gases, then good separation power is achieved, but explosive gas mixtures form in the distillation zone
Solution Approach 1:
Nitrogen is added to the distillation column before the oxygen concentration can build up to explosive levels, preemptively preventing the formation of explosive mixtures by maintaining oxygen below 12% concentration
Solution Approach 2:
Nitrogen acts as an intermediary substance that mediates between the oxygen and methane, preventing direct interaction that would create explosive conditions while allowing the distillation separation to proceed
4Loss of substance
If the gas phase from decompression is used as dilution stream, then nitrogen consumption is reduced and methane loss is minimized, but additional separation equipment is required
Solution Approach 1:
The gas phase is separated from the liquid phase through decompression before the distillation process begins, preparing the nitrogen-rich gas for reuse as dilution stream in advance
Solution Approach 2:
The decompression separation function is combined with the feed preparation process, integrating multiple functions into a coordinated sequence that reduces overall equipment 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
The process effectively reduces oxygen concentrations below explosive limits, decreases nitrogen consumption, and enhances methane recovery rates, making the process safer and more economically viable for biomethane production by avoiding the need for external nitrogen and minimizing methane loss.
Implementation Method 1
the feed stream is cooled to produce a cooled stream
Implementation Method 2
the cooled stream is sent to a decompression member to separate a gas phase and a liquid phase
Implementation Method 3
cryogenic distillation which can achieve a good separation power between methane on the one hand, recovered at the column bottom and oxygen and nitrogen on the other hand recovered at the column head, because of volatility differences between these components
Data Source
AI summary
A process for cryogenic separation of a feed stream containing methane and air gases in which: the feed stream is cooled in order to produce a cooled stream, at least one portion of the cooled stream is sent to one level of a distillation column, a bottom stream is drawn off from the distillation column, the bottom stream being enriched in methane relative to the feed stream, a stream enriched in oxygen and in nitrogen relative to the feed stream is drawn off from the distillation column, at least one noncombustible dilution stream that is more volatile than oxygen is introduced into the distillation column at at least one level lower than the one at which the cooled stream is introduced. The dilution stream is extracted from the feed stream. Facility for producing biomethane by purification of biogases derived from non-hazardous waste storage facilities (NHWSF) implementing the process.