Cryogenic Methane Separation With Nitrogen Flammability Control
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Solution Overview
Problem
Cryogenic distillation for methane purification from biogas faces the challenge of flammability risks due to oxygen accumulation in the distillation column, which existing methods fail to adequately address, particularly in ensuring operation outside the flammability zone.
Innovation Solution
Incorporating a nitrogen-rich flow into the distillation column, specifically at the bottom, to enrich nitrogen composition and avoid the flammability zone, thereby preventing oxygen accumulation and ensuring safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cryogenic distillation is used for methane purification, then high purification yield is achieved, but oxygen accumulation creates flammability risks
Solution Approach 1:
A nitrogen-rich stream is introduced as an intermediary substance into the distillation column to prevent oxygen accumulation. The nitrogen acts as a buffer gas that displaces oxygen from the flammability zone, allowing the distillation process to continue at high efficiency without creating explosive conditions.
Solution Approach 2:
The patent creates an inert atmosphere within the distillation column by introducing nitrogen-rich gas. This inert environment prevents the formation of flammable mixtures between methane and oxygen, allowing the cryogenic distillation process to operate safely while maintaining high purification yields.
2Reliability
If nitrogen-rich flow is added to prevent flammability, then safety is improved, but process complexity increases
Solution Approach 1:
The nitrogen-rich stream serves multiple functions simultaneously: it prevents oxygen accumulation in the flammability zone, maintains proper column pressure, and facilitates continuous operation. This multi-functionality reduces the need for additional separate safety systems, thereby limiting the increase in process complexity.
Solution Approach 2:
The patent modifies the compositional parameters of the feed stream by adding nitrogen-rich gas, changing the overall gas composition to remain outside the flammability zone. This parameter change approach is simpler than installing complex safety monitoring and control systems.
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 effectively prevents flammability issues by maintaining the distillation column operation outside the flammability zone, ensuring safe and efficient methane purification while maintaining high yields and minimizing maintenance.
Implementation Method 1
Another solution for the separation is cryogenic distillation as described in WO-A-09/004207
Implementation Method 2
the feed stream is sent to a condenser-reboiler where it partially vaporizes the bottom liquid to form a vaporized gas, the fully or partially liquefied feed stream is sent from the condenser-reboiler to the column
Implementation Method 3
the vaporized gas is mixed with nitrogen-rich flow
Implementation Method 4
the feed stream is sent to a condenser-reboiler where it partially vaporizes the bottom liquid to form a vaporized gas
Data Source
Figure 1
Figure 2
AI summary
In a process for the cryogenic separation of a methane-rich feed stream containing between 3 and 35% of oxygen and also nitrogen, the feed stream is cooled in order to produce a cooled stream, at least one portion of the cooled stream is sent to a distillation column (6), a bottom stream is withdrawn from the distillation column, the bottom stream being enriched in methane compared to the feed stream, a stream enriched in oxygen compared to the feed stream is withdrawn from the distillation column, and a nitrogen-rich stream (20, 21) is sent to the column.