Cryogenic Nitrogen Extraction With Dual Expansion for Higher Liquid Yield
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Solution Overview
Problem
Current air separation processes are limited in producing large amounts of liquid nitrogen, typically achieving less than 5 mole percent, and existing methods for increasing liquid production are either inefficient or require high investment costs.
Innovation Solution
A method involving a modified double-column process with a second expansion machine and efficient heat exchanger design to generate cold for higher liquid production, allowing for 60% nitrogen yield and recovery of over 90 mole % gaseous nitrogen, operated under pressures of 8 to 9 bar, with optional use of generator turbines or compressor stages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a modified double-column process operated under higher pressure is used to obtain large amounts of compressed nitrogen, then the nitrogen production quantity increases, but the liquid production capability is limited to less than 5 mole percent
Solution Approach 1:
The invention divides the nitrogen production system into two separate expansion machines: a first expansion machine for producing compressed nitrogen and a second expansion machine for producing liquid nitrogen. This segmentation allows each machine to be optimized for its specific function, enabling the system to produce both large amounts of compressed nitrogen and significant quantities of liquid nitrogen (6 to 10 mol % or more) simultaneously, thereby resolving the contradiction between compressed nitrogen production and liquid nitrogen productivity.
2Device complexity
If a single condenser-evaporator system is used in conventional double-column processes, then the system complexity is low, but the cold generation efficiency is insufficient for high liquid production
Solution Approach 1:
The invention introduces a second condenser-evaporator system in addition to the main condenser, creating specialized cooling zones for different nitrogen streams. The second condenser-evaporator is specifically designed to cool the second compressed nitrogen stream from the second expansion machine, enabling efficient liquid nitrogen production without significantly increasing overall system complexity and while minimizing energy losses through targeted heat exchange.
3Ease of operation
If the inlet temperatures of expansion machines are not optimized, then the system operation is simple, but thermodynamic losses increase
Solution Approach 1:
The invention optimizes the inlet temperatures of the two expansion machines as key parameters: the first expansion machine receives nitrogen at a first intermediate temperature, while the second expansion machine receives nitrogen at a second intermediate temperature that is at least 10 K higher. This parameter optimization minimizes thermodynamic losses in the expansion process while maintaining simple system operation, as the temperature differences are built into the heat exchanger design rather than requiring complex real-time control.
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 method achieves efficient liquid nitrogen production of 6 to 10 mol % with high nitrogen yield, addressing the limitations of existing processes by minimizing additional effort and thermodynamic losses, suitable for applications requiring large amounts of pressurized nitrogen and liquid product.
Implementation Method 1
A 'main heat exchanger' serves to cool feed air in indirect heat exchange with return streams from the distillation column system
Implementation Method 2
The condensation (liquefaction) of the first fluid stream is carried out in the liquefaction chamber
Implementation Method 3
the evaporation of the second fluid stream is carried out in the evaporation chamber
Implementation Method 4
A second stream of compressed nitrogen is drawn off from the top of the high-pressure column and expanded in a second expansion machine to a pressure that still allows this stream to be drawn off as a pressure product
Data Source
AI summary
The method and the device serve to produce compressed nitrogen and liquid nitrogen by low-temperature separation of air in a distillation column system which has a high-pressure column (9) and a low-pressure column (10) and a main condenser (11) and a low-pressure column top condenser (12), both of which have are designed as a condenser-evaporator. Air (AIR) is compressed in a main air compressor (2), cleaned (6), cooled in a main heat exchanger (8) and introduced (8) into the high-pressure column (9). A first portion (44) of the gaseous overhead nitrogen from the low pressure column (10) is withdrawn as the first compressed nitrogen product (18, 19, PGAN). A second portion (45) of the gaseous nitrogen at the top of the low-pressure column (10) is at least partially liquefied in the liquefaction space of the low-pressure column top condenser (12). The vapor generated in the evaporation chamber of the low-pressure column top condenser (12) is drawn off as a residual gas stream (26) and expanded in a first expansion machine (28) to perform work. A second stream of compressed nitrogen (17) from the top of the high-pressure column (9) is expanded to produce work in a second expansion machine (41) and then drawn off as a second compressed nitrogen product (43, 19, PGAN). A portion (47) of the nitrogen (46) liquefied in the low pressure column top condenser (12) is withdrawn as liquid nitrogen product (PLIN).