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
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Solution Overview
Problem
Current cryogenic separation methods for methane from gas mixtures containing air gases like nitrogen and oxygen face challenges in avoiding explosive vapor mixtures and require additional processing steps, leading to economic and safety issues, and struggle with carbon dioxide and water content that can clog cryogenic exchangers.
Innovation Solution
A cryogenic separation process where the feed stream is pre-treated to reduce carbon dioxide and water content, and oxygen is diluted using nitrogen from the feed stream, rather than an external source, within the distillation column, ensuring concentrations remain outside explosive zones and avoiding clogging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If cryogenic distillation is used to separate methane from air gases, then separation efficiency is improved, but the risk of forming explosive vapor mixtures increases
Solution Approach 1:
The patent applies preliminary action by pre-cooling the feed stream and pre-establishing the cryogenic environment before the distillation process begins. The feed stream is cooled to cryogenic temperatures in a heat exchanger before entering the distillation column, ensuring that the separation process can proceed safely without forming explosive vapor mixtures from the start
Solution Approach 2:
The patent creates an inert environment by maintaining the entire distillation system at cryogenic temperatures where methane and air gases remain in liquid or controlled vapor states. The cryogenic conditions prevent the formation of explosive vapor mixtures by keeping the system in a non-flammable state throughout the separation process
2Reliability
If external nitrogen is used to dilute oxygen in the distillation column, then explosive mixture prevention is improved, but nitrogen consumption and operating costs increase
Solution Approach 1:
The patent applies self-service by using the nitrogen component already present in the feed stream for dilution purposes, rather than requiring external nitrogen supply. The nitrogen is separated from the feed stream during the cryogenic distillation process itself and then reused as a diluent in the distillation column, making the system self-sufficient and eliminating additional nitrogen consumption
Solution Approach 2:
The patent recovers nitrogen that would otherwise be discarded or lost during the separation process. The nitrogen component is extracted from the feed stream during distillation and then reused as a diluent to prevent explosive mixtures, transforming a potential waste stream into a valuable process resource that reduces operating costs
3Device complexity
If carbon dioxide and water are not removed before cryogenic separation, then process complexity is reduced, but clogging of cryogenic exchangers occurs
Solution Approach 1:
The patent applies preliminary action by removing carbon dioxide and water from the feed stream before the cryogenic separation process begins. This pre-treatment step prevents these components from freezing and clogging the cryogenic exchangers and distillation column during the low-temperature separation process
Solution Approach 2:
The patent applies preliminary anti-action by removing carbon dioxide and water in advance to prevent the harmful effect of clogging. The pre-treatment step counteracts the potential problem of freeze-up by eliminating the components that would cause it before they can enter the cryogenic separation system
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 reduces nitrogen consumption, minimizes methane loss, and prevents the formation of explosive vapor mixtures, while allowing for efficient separation of methane from air gases, ensuring a safe and cost-effective process for producing enriched methane flows.
Implementation Method 1
A flow containing methane, carbon dioxide, nitrogen and/or oxygen and more generally gases from the air, is cooled to a temperature below -100°C
Implementation Method 2
cryogenic distillation, which makes it possible to have a good separating power between the methane on the one hand, recovered in the column tank and the oxygen and the nitrogen on the other hand, recovered at the head of the column, thanks to the differences in volatility between these components
Implementation Method 3
the presence of oxygen, the volatility of which is between that of methane and that of nitrogen, leads to this compound tending to concentrate in the distillation zone, even for low oxygen contents. in the column load. The increase in the concentration of oxygen in the vapor phase, added to the decrease in the concentration of methane in the vapor phase, can lead to a mixture of vapor which is, due to its compositions, explosive
Data Source
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AI summary
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, characterized in that 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.