Process for cryogenic separation of a feed stream containing methane and air gases, facility for producing biomethane by purification of biogases derived from non-hazardous waste storage facilities (NHWSF) implementing the process
Find Innovative SolutionsGenerate Solutions
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, while also regenerating adsorbents efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external nitrogen is used to dilute oxygen in the distillation column, then explosive gas mixtures are prevented, but operating costs increase due to nitrogen consumption
Solution Approach 1:
The system uses its own feed stream to provide the dilution nitrogen, extracting nitrogen directly from the biogas feed before the distillation column. This self-service approach eliminates the need for external nitrogen supply, reducing operating costs while maintaining safety by preventing explosive gas mixtures in the distillation column
Solution Approach 2:
The nitrogen extraction unit is integrated with the distillation column system, combining the dilution nitrogen supply function with the existing biogas processing flow. The nitrogen is extracted from the feed stream and fed back to the distillation column, merging multiple functions into a unified process that reduces external resource requirements
2Manufacturing precision
If cryogenic distillation is used to separate methane from air gases, then good separation power is achieved, but the risk of forming explosive gas mixtures increases
Solution Approach 1:
Nitrogen is added to the distillation column before the methane-rich vapor can accumulate to explosive concentrations. This preliminary action of dilution prevents the formation of explosive gas mixtures by maintaining oxygen and methane concentrations below explosive limits throughout the distillation process
Solution Approach 2:
Nitrogen creates an inert atmosphere in the distillation column by diluting both oxygen and methane concentrations. This inert environment prevents combustion and explosion by ensuring that neither oxygen nor methane reaches concentrations required for explosive reactions, while still allowing cryogenic distillation to achieve good separation power
3Manufacturing precision
If pressure modulated adsorption is used to remove air gases, then oxygen and nitrogen concentration is reduced, but methane recovery rate decreases
Solution Approach 1:
The invention changes the approach from adsorption-based removal to cryogenic distillation with nitrogen dilution. By changing the separation mechanism and operating parameters (temperature, pressure, and composition control), the system achieves both effective impurity removal and high methane recovery rates that are not attainable with pressure modulated adsorption alone
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 the separation process operates within safe limits, reduces operating costs, and enhances methane recovery rates by using internally sourced nitrogen for dilution, thereby preventing explosive conditions and optimizing the production of a methane-enriched stream suitable for biomethane production.
Implementation Method 1
the feed stream is cooled to a temperature below -50°C, preferably below -80°C, more preferably below -100°C
Implementation Method 2
the cooled stream is condensed, preferably in a heat exchanger
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
Implementation Method 4
at least one dilution stream that is incombustible and more volatile than oxygen (meaning a stream containing essentially nitrogen) is added to the distillation column at least one level below the level at which the cooled stream is added
Implementation Method 5
the use of gas permeation membranes combined with the treatment of impurities by adsorption
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.