Dual column nitrogen producing air separation unit with split kettle reboil and integrated condenser-reboiler
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Solution Overview
Problem
Large-scale nitrogen producing cryogenic air separation units face challenges in improving nitrogen recovery and reducing operating and capital costs, particularly in systems requiring liquid nitrogen production, where conventional turbine arrangements lead to high power costs and impractical rangeability.
Innovation Solution
A dual column air separation unit with an integrated condenser-reboiler arrangement, recycling vapor from condenser-reboilers to the feed and purified air streams, and utilizing multiple condenser-reboilers to enhance heat transfer and refrigeration efficiency, including a third condenser-reboiler associated with the lower pressure column for improved nitrogen recovery and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional upper column turbine arrangement is used for refrigeration, then the air separation unit can operate, but power consumption increases and rangeability becomes impractical for liquid nitrogen production
Solution Approach 1:
The invention divides the refrigeration system into multiple independent turbine arrangements: an upper column turbine for the high pressure column and a lower column turbine for the low pressure column. This segmentation allows each turbine to be optimized for its specific column and operating conditions, improving overall energy efficiency and enabling flexible operation for liquid nitrogen production without the limitations of a single turbine arrangement.
2Reliability
If a triple distillation column arrangement is used, then nitrogen recovery increases and power consumption decreases, but capital costs increase due to additional columns, condenser/reboilers, and compressors
Solution Approach 1:
The invention merges the functions of multiple condenser/reboiler units into an integrated condenser/reboiler arrangement that serves both the high pressure and low pressure columns. This integration maintains the enhanced nitrogen recovery and reduced power consumption benefits of a multi-column system while reducing capital costs by eliminating redundant equipment and simplifying the overall system configuration.
Solution Approach 2:
The integrated condenser/reboiler unit performs multiple functions simultaneously: it acts as a condenser for the high pressure column, a reboiler for the low pressure column, and provides thermal coupling between the two columns. This multi-functionality achieves the performance benefits of a triple column arrangement with the capital cost structure of a dual column system.
3Productivity
If multiple condenser-reboilers with vapor recycling are used, then heat transfer and refrigeration efficiency improve, but system complexity increases
Solution Approach 1:
The system uses vapor recycling where vapor from the condenser-reboilers is recycled back to the feed air stream and/or compressed purified air streams. This self-service approach allows the system to utilize its own byproduct (vapor) to enhance heat transfer efficiency and refrigeration performance without requiring external energy inputs, thereby improving productivity while managing system complexity through resourceful internal cycling.
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
The solution enhances nitrogen recovery and reduces power consumption and capital costs by optimizing the heat transfer and refrigeration processes in the dual column system, improving the efficiency and economic viability of large-scale nitrogen production.
Implementation Method 1
a main heat exchange system configured to cool the compressed and purified air stream to temperatures suitable for fractional distillation
Implementation Method 2
the main condenser is driven by reboiling a portion of the lower pressure bottoms liquid... condenses a portion of the nitrogen enriched overhead from the higher pressure column against a split kettle stream
Implementation Method 3
temperatures suitable for fractional distillation... the higher pressure column is configured to receive the cooled, compressed, purified air stream and produce a nitrogen enriched overhead and an oxygen-enriched kettle stream
Implementation Method 4
an adsorption based pre-purifier unit configured for removing impurities from the compressed air stream and producing a compressed, purified air stream
Data Source
AI summary
Enhancements to a dual column, nitrogen producing cryogenic air separation unit are provided. Such enhancements include an improved air separation cycle that uses multiple condenser-reboilers and recycles a portion of the vapor from one or more of the condenser-reboilers to the incoming feed stream and or the compressed purified air streams to yield improvements in such dual column, nitrogen producing cryogenic air separation units. The multiple condenser-reboilers preferably include an integrated condenser-reboiler arrangement comprising a heat exchanger having a set of nitrogen condensing passages, a first set and second set of boiling passages, and a phase separator.