Cryogenic Air Separation with Constant-Flow Adsorber Repressurization
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Solution Overview
Problem
Current air separation processes face challenges in maintaining constant air flow and compressor capacity during repressurization, leading to process upsets and increased capital expenditures due to varying air flow rates and compositions.
Innovation Solution
The method involves using an external dry gas, such as nitrogen or purified air, to repressurize adsorbers without diverting purified air from the online adsorber or altering the main air compressor flow rate, ensuring a constant air flow to the cold box and minimizing capital expenditures by maintaining consistent process conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If purified air is diverted to repressurize the adsorber during regeneration, then the adsorber can be repressurized, but the air flow to the cold box varies and process upsets occur
Solution Approach 1:
A dry gas buffer tank is introduced as an intermediary storage system between the air compressor and the adsorber. Compressed dry air is stored in the buffer tank and then used to repressurize the adsorber during regeneration, preventing direct diversion of purified air from the cold box and maintaining stable air flow composition to the cold box.
Solution Approach 2:
Dry air is pre-compressed and stored in the buffer tank before regeneration is needed. This preliminary action ensures that when regeneration occurs, the adsorber can be repressurized using pre-prepared dry gas without affecting the continuous supply of purified air to the cold box.
2Ease of operation
If the main air compressor flow rate is varied to accommodate repressurization, then repressurization can be performed, but capital expenditures increase due to varying air flow rates
Solution Approach 1:
The dry gas buffer tank serves as a decoupling intermediary that separates the compressor operation from the repressurization operation. The compressor maintains a constant flow rate charging the buffer tank, while repressurization is performed using stored gas, eliminating the need for variable compressor capacity and reducing capital expenditures.
Solution Approach 2:
The system uses its own compressed dry air inventory (self-produced by the compressor during normal operation) to service the repressurization need during regeneration, without requiring external variable capacity adjustments or additional equipment.
3Ease of operation
If purified air from the online adsorber is used for repressurization, then repressurization is achieved, but process upsets occur due to changing air flow rates
Solution Approach 1:
The buffer tank acts as a mediator that provides dry gas for repressurization without requiring diversion of purified air from the online adsorber to the cold box. This maintains reliable and stable process conditions in the cold box while enabling complete regeneration operation.
Solution Approach 2:
Dry gas is prepared and stored in advance in the buffer tank, so when regeneration is needed, repressurization can proceed using pre-stored gas rather than diverting purified air during the regeneration process, thereby maintaining process stability.
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 the main air compressor to operate at a constant capacity and maintain a consistent air flow to the cold box, reducing process upsets and capital expenditures related to warm-end equipment, while maintaining stable process conditions within the cold box.
Implementation Method 1
purifying a compressed wet air stream of water and carbon dioxide with a front end purification system to produce a dry air stream
Implementation Method 2
introducing the dry air stream to a cold box under conditions effective to separate air into a nitrogen-enriched stream and an oxygen-enriched stream
Data Source
AI summary
A method and apparatus for the production of air gases by the cryogenic separation of air with front end purification and air compression can include using an available compressed dry gas such as nitrogen, oxygen, stored purified air, or synthetic air to repressurize the adsorber without diverting any of the purified air just exiting the currently on-line adsorber or changing the flow rate of the main air compressor or air sent to the cold box. This enables the main air compressor (MAC) to operate at a relatively constant flow rate while also sending a relatively constant air flow to the cold box during this repressurization step, thereby reducing the risks of process upsets and minimizing capital expenditures related to the MAC and other warm-end equipments.