Cryogenic Air Separation Flow Split for High-Pressure Gas Efficiency
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Solution Overview
Problem
Current methods for low-temperature air decomposition in air separation plants are inefficient in terms of energy usage, particularly in high air pressure (HAP) processes, where compressing air to high pressures leads to suboptimal heat exchange and energy consumption.
Innovation Solution
Introducing an additional throttle flow through the cold part of the main heat exchanger at a lower pressure, and optimizing the heat exchange process by cooling and expanding air flows in a specific manner, including the use of multiple turbines and heat exchangers to enhance heat transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If air is compressed to high pressures in HAP processes, then the product gas can be obtained at high pressure, but energy consumption increases due to suboptimal heat exchange
Solution Approach 1:
The air flow is divided into multiple partial flows with different pressures. A first partial flow is compressed to high pressure (e.g., 20-30 bar) for product generation, while a second partial flow remains at lower pressure (e.g., 6-15 bar) to provide efficient heat exchange in the cold section of the main heat exchanger, avoiding the energy penalty of compressing all air to high pressure
Solution Approach 2:
The invention changes the pressure parameter distribution in the system by introducing a second partial flow at intermediate pressure (6-15 bar) that is optimized for heat exchange efficiency. This creates a favorable heat exchange diagram where heat transfer occurs at progressively decreasing temperature differences, reducing the work required by the main compressor
2Device complexity
If a single machine compressor is used for all air compression, then device complexity is reduced, but heat exchange efficiency deteriorates
Solution Approach 1:
The air compression and heat exchange process is segmented into two parallel paths: one for high-pressure product generation and another for efficient heat exchange. This segmentation allows the single compressor to deliver different pressure streams that optimize both mechanical simplicity and thermal efficiency
Solution Approach 2:
The second partial flow acts as an intermediary medium that provides the necessary cold heat exchange capacity without requiring high-pressure compression. It mediates between the compressor output and the distillation columns, enabling efficient heat recovery and reducing the overall energy consumption of the system
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 improves energy efficiency by creating a favorable heat exchange diagram, reducing energy consumption, especially when producing nitrogen at pressures between 7 and 15 bar, and allows for further optimization of the heat exchange process in the main heat exchanger.
Implementation Method 1
optimizing the heat exchange process by cooling and expanding air flows in a specific manner, including the use of multiple turbines and heat exchangers to enhance heat transfer efficiency
Implementation Method 2
Introducing an additional throttle flow through the cold part of the main heat exchanger at a lower pressure, and optimizing the heat exchange process by cooling and expanding air flows
Implementation Method 3
including the use of multiple turbines and heat exchangers to enhance heat transfer efficiency
Implementation Method 4
Methods and devices for the low-temperature decomposition of air are known, for example, from Hausen/Linde, Tieftemperaturtechnik, 2nd edition 1985, Chapter 4 (pages 281 to 337)
Implementation Method 5
The distillation column system of such a plant can be designed as a two-column system (for example as a classic Linde double-column system)
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The method and the device are used to obtain a compressed gas product (72; 73) by means of low-temperature decomposition of air in a distillation column system which has a high-pressure column (21) and a low-pressure column (22). All of the feed air is compressed in a main air compressor (2) to a first pressure which is at least 4 bar higher than the operating pressure of the high-pressure column (21). A first partial stream (8, 11, 14) of the feed air (7) compressed in the main air compressor (2) is cooled to an intermediate temperature in a main heat exchanger (13) and expanded to perform work in a first air turbine (15). At least a first portion of the work-expanded first substream (16) is introduced into the distillation column system (40; 18, 19, 20). A second partial stream (12, 27, 29, 30) of the feed air compressed in the main air compressor (2) is post-compressed in a first post-compressor (9), which is driven in particular by the first turbine (15), to a second pressure that is higher than the first pressure, cooled to an intermediate temperature in the main heat exchanger (13), is post-compressed in a second post-compressor (28), which operates as a cold compressor and is driven in particular by the second turbine (38), to a third pressure which is higher than that second pressure is cooled in the main heat exchanger (13) and then expanded (31) and introduced into the distillation column system (32). A third partial flow (436, 37) of the feed air (7) compressed in the main air compressor (2) is cooled to an intermediate temperature in the main heat exchanger (13) and expanded to perform work in a second air turbine (38). At least a first portion (339) of the work-expanded third partial flow is introduced into the distillation column system (340). A first product stream (69; 75) is withdrawn in liquid form from the distillation column system and subjected to a pressure increase (71; 76) to a first product pressure. The first product stream is vaporized or pseudo-vaporized and heated under the first product pressure in the main heat exchanger (13). The heated first product stream (72; 77) is obtained as the first compressed gas product (GOX IC; GAN IC). The third partial flow (37) is expanded in the second air turbine (38) to a pressure which is at least 1 bar higher than the operating pressure of the high-pressure column (21). At least a first part (339) of the work-expanded third partial stream is further cooled in the main heat exchanger (13), liquefied and then expanded (341) and introduced into the distillation column system.