Process and plant for the combination production of a mixture of hydrogen and nitrogen and also of carbon monoxide by cryogenic distillation and cryogenic scrubbing
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Solution Overview
Problem
Existing methane scrubbing processes for synthesis gas require sufficient methane levels to maintain efficiency, leading to methane losses and increased energy consumption when methane is scarce, and often result in reduced CO extraction yield or nitrogen contamination in CO products.
Innovation Solution
A process is introduced that adds a nitrogen scrubbing section to the top of the scrubbing column, allowing for sequential scrubbing with methane and nitrogen, and includes a stripping column to recover lost methane, enabling efficient production of hydrogen, nitrogen, carbon monoxide, and methane using cryogenic distillation and scrubbing, even with low methane content in the synthesis gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If methane scrubbing is used to separate synthesis gas, then hydrogen and nitrogen mixture can be produced, but methane is lost in the overhead gas requiring sufficient methane content in feed gas
Solution Approach 1:
The patent extracts methane from the overhead gas stream using a stripping column, separating it from the hydrogen-nitrogen mixture. This allows methane to be recovered and reused as scrubbing liquid, eliminating the need for high methane content in feed gas and preventing methane loss to flares.
Solution Approach 2:
Instead of discarding methane-containing overhead gas, the patent recovers methane through stripping with caustic soda solution, then condenses and reuses it as scrubbing liquid in the methane scrubbing column, creating a closed-loop system that minimizes methane loss.
2Device complexity
If partial condensation process is used instead of methane scrubbing, then equipment complexity is reduced, but CO extraction yield is significantly reduced
Solution Approach 1:
The patent merges methane scrubbing with caustic soda washing by using the caustic soda solution as stripping liquid in the stripping column. This combines two functions (CO2 removal and methane recovery) into a integrated system, maintaining high CO extraction yield while managing equipment complexity through functional integration.
3Adaptability or versatility
If nitrogen is added to increase H2/N2 ratio for ammonia synthesis, then ammonia synthesis capability is improved, but CO product becomes contaminated with nitrogen
Solution Approach 1:
The patent segments the scrubbing process into distinct sections: methane scrubbing at the bottom, caustic soda washing in the middle, and nitrogen scrubbing at the top. This segmentation allows nitrogen to be added selectively in the top section to adjust H2/N2 ratio without contaminating the CO product drawn from the bottom section.
Solution Approach 2:
Different sections of the scrubbing column have different liquid compositions and functions: methane-rich liquid at the bottom for CO recovery, caustic soda solution in the middle for CO2 removal, and nitrogen-rich liquid at the top for H2/N2 ratio adjustment. This local quality differentiation enables simultaneous achievement of CO purity and ammonia synthesis capability.
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 allows for the use of methane scrubbing with low methane levels, reduces energy consumption, and minimizes nitrogen contamination in CO products, achieving higher CO yield and reducing the need for additional gas imports, while using a single cold box and smaller equipment.
Implementation Method 1
a gas mixture containing at least hydrogen, carbon monoxide and methane is cooled in a heat exchanger
Implementation Method 2
a methane-rich liquid is introduced at a first intermediate level of the scrubbing column as first scrubbing liquid, at least one nitrogen-rich liquid is introduced at a level higher than the first level of the scrubbing column as second scrubbing liquid
Implementation Method 3
a mixture of hydrogen and nitrogen is drawn off as overhead gas from the scrubbing column
Implementation Method 4
a bottoms liquid is drawn off from the scrubbing column and sent to a stripping column
Implementation Method 5
a bottoms liquid is drawn off from the stripping column and sent to a column for separating carbon monoxide and methane, a fluid rich in carbon monoxide is drawn off from the separating column
Data Source
AI summary
Process for the combined production of a mixture of hydrogen and nitrogen, and of carbon monoxide by cryogenic distillation and cryogenic scrubbing, wherein a methane-rich liquid is introduced at a first intermediate level of a scrubbing column as first scrubbing liquid and at least one nitrogen-rich liquid is introduced at a level higher than the first level of the scrubbing column as second scrubbing liquid and a mixture of hydrogen and nitrogen is drawn off as overhead gas from the scrubbing column.