Double-Column Nitrogen Separation for Lower Air and Power Use
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Solution Overview
Problem
Current nitrogen generating apparatuses face challenges in reducing the amount of raw material air, power consumption, and facility costs, with the A/N ratio close to its limit, making further reductions difficult.
Innovation Solution
A double rectification method is employed, where compressed air is cooled and cryogenically separated in a high-pressure column, with liquid air transferred to a low-pressure column for further separation, using a difference in boiling points to enhance nitrogen yield, and liquid nitrogen or oxygen is used as a coolant to supplement heat loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a single rectification type nitrogen generating apparatus is used to reduce the amount of raw material air, then the A/N ratio can be reduced, but the A/N ratio approaches the limit of approximately 2.1 and further reduction becomes difficult
Solution Approach 1:
The rectification column is divided into two separate columns operating at different pressures: a high-pressure column (first rectification column) and a low-pressure column (second rectification column). The high-pressure column performs initial separation to produce liquid air, which is then fed to the low-pressure column for further nitrogen separation. This segmentation allows each column to operate optimally at its respective pressure, overcoming the limitations of a single column system and achieving nitrogen yields beyond the traditional A/N ratio of 2.1.
2Use of energy by moving object
If the amount of raw material air is reduced to lower power consumption and facility costs, then operating costs decrease, but the nitrogen production capacity is limited by the A/N ratio approaching 2.1
Solution Approach 1:
The system changes the operating pressure parameter by using two columns at different pressures. The high-pressure column operates at elevated pressure for initial separation, and the low-pressure column operates at lower pressure for final nitrogen production. This parameter change allows the system to achieve higher nitrogen yields per unit of raw material air, thereby reducing power consumption and facility costs while maintaining or increasing nitrogen production capacity.
3Temperature
If liquid nitrogen is injected as a coolant in the rectification column, then the column temperature is maintained for cryogenic separation, but coolant consumption increases facility costs
Solution Approach 1:
The system uses self-service cooling where the process itself provides the cooling needed. Liquid air produced in the high-pressure column is fed to the low-pressure column, and the evaporation of this liquid air provides the necessary cooling for cryogenic separation. Additionally, the cold nitrogen gas produced in the low-pressure column is used to cool the incoming compressed air in the heat exchanger. This eliminates or reduces the need for external liquid nitrogen coolant injection, thereby reducing coolant consumption and facility costs while maintaining the required column temperatures.
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 significantly reduces the amount of raw material air, power consumption, and facility costs by improving nitrogen yield and optimizing coolant usage, achieving an A/N ratio of approximately 1.4 and minimizing coolant injection.
Implementation Method 1
introducing the compressed air passed through the adsorption columns 34 through a supply pipe 35 into a main heat exchanger 36 to heat-exchange the compressed air with a refrigerant therein, thereby cooling the compressed air down to an ultra low temperature
Implementation Method 2
introducing the compressed air cooled down to the ultra low temperature through an inlet pipe 37 into a rectification column 38 to cryogenically liquefy and separate the compressed air therein, thereby producing a product nitrogen gas
Implementation Method 3
cryogenically separating the compressed air introduced into the high-pressure column by using a difference in boiling point between components in the compressed air
Implementation Method 4
Part of the nitrogen gas stored in the upper portion of the rectification column 38 is fed through a first reflux pipe 43a into the above-mentioned condenser 42a
Implementation Method 5
The stored liquid air (containing 50 to 70% N2; and 30 to 50% O2) 41 accumulated in the bottom portion of the rectification column 38 is fed through a feed pipe 44 with an expansion valve 44a into the dephlegmator 42, and is gasified to cool the internal temperature down to a temperature not greater than the boiling point of liquid nitrogen
Data Source
AI summary
There is provided a method of generating nitrogen which includes cryogenically separating compressed air introduced into a high-pressure column 11, storing liquid air 13 in a bottom portion of the high-pressure column 11 and taking nitrogen in gaseous form from an upper portion of the high-pressure column 11, introducing the liquid air 13 stored in the bottom portion of the high-pressure column 11 into a low-pressure column12, cryogenically separating the liquid air 13 introduced into the low-pressure column 12 and storing oxygen-enriched liquid air 22 in a bottom portion of the low-pressure column 12 and taking nitrogen in gaseous form from an upper portion of the low-pressure column 12 as a product gas. Liquid air 13 taken through an extraction pipe 20 is introduced into a portion of a rectification part 12a of the low-pressure column 12 in which the number of theoretical plates from a column bottom side is set within the range of one to ten.