Method and device for the low-temperature separation of air at variable energy consumption
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Solution Overview
Problem
Air separation plants face challenges in maintaining efficient operation across varying production levels, particularly when reducing oxygen production, as the energy demand for other products like nitrogen and argon is not adequately met due to limited compressor pressure and design constraints in High Air Pressure (HAP) processes.
Innovation Solution
The method involves redirecting a portion of the feed air past the distillation column system, allowing it to be returned to the main air compressor, thereby increasing energy efficiency and maintaining liquid production by avoiding throttling and using a second air turbine to enhance internal compression pressure without external energy, allowing for flexible operation across different load ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the main air compressor pressure is increased to meet energy demand for other products when oxygen production is reduced, then energy efficiency for nitrogen and argon production improves, but the compressor reaches its maximum pressure limit and cannot provide sufficient energy
Solution Approach 1:
The air flow is divided into multiple streams: a first stream passes through the distillation columns for oxygen production, while a second stream bypasses the columns and is redirected to the compressor inlet. This segmentation allows independent control of energy supply to different product streams, enabling the bypass stream to provide additional compression energy when oxygen demand decreases.
Solution Approach 2:
The main air compressor serves dual functions: it compresses air for the distillation columns to produce oxygen, and simultaneously compresses the bypass air stream to provide energy for nitrogen and argon production. This multi-functionality allows the single compressor to meet energy demands across varying production levels without requiring additional compression equipment.
2Adaptability or versatility
If a portion of feed air is redirected past the distillation column system and returned to the compressor, then energy distribution flexibility improves for variable production levels, but the system complexity increases with additional flow control mechanisms
Solution Approach 1:
The system incorporates dynamic flow control valves and switches that can adjust the bypass air stream proportion based on real-time oxygen production demands. This dynamic adjustment capability allows the system to adapt to varying production levels (e.g., 100% to 70% oxygen production) while automatically optimizing energy distribution to maintain nitrogen and argon production.
Solution Approach 2:
The control system monitors oxygen production levels and automatically adjusts the bypass stream flow rate accordingly. When oxygen production decreases, the control system increases the bypass stream to provide additional compression energy, maintaining overall system energy efficiency without requiring manual intervention or complex external control systems.
3Loss of energy
If the bypass air stream is used to provide energy for internal compression, then external energy consumption decreases, but the pressure management complexity increases to maintain proper distillation column operation
Solution Approach 1:
The bypass air stream, after being compressed by the main air compressor, is expanded through a turbine that drives the oxygen pump. This self-service mechanism uses the compressed bypass air to provide mechanical work for internal circulation and product delivery, reducing external energy consumption while the pressure management is handled automatically by the coordinated operation of compression and expansion stages.
Solution Approach 2:
The system utilizes pressure and temperature parameter changes throughout the compression and expansion cycles. The bypass stream undergoes compression (pressure increase), cooling, expansion (pressure decrease with work output), and reheating, with these parameter changes carefully managed to ensure proper distillation column operation while maximizing energy recovery and minimizing external energy requirements.
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 enables the air separation plant to maintain energy efficiency and produce other air separation products consistently, even at reduced oxygen production levels, by optimizing energy distribution and pressure management within the system.
Implementation Method 1
The first partial stream of feed air compressed in the main air compressor is cooled in a main heat exchanger
Implementation Method 2
The cooled first partial stream is expanded in a first air turbine to produce work
Implementation Method 3
a first amount of feed air compressed in the main air compressor is compressed upstream of its introduction into the main heat exchanger in a first booster compressor
Implementation Method 4
a first amount of feed air is compressed in the main air compressor
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)
Implementation Method 6
a liquid pressurized product stream is evaporated against a heat transfer medium and finally obtained as an internally compressed compressed gas product
Implementation Method 7
Against the (pseudo-)evaporating product stream, a heat transfer medium under high pressure is liquefied
Data Source
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AI summary
The invention relates to a method and to a device used to variably obtain a compressed-gas product (72; 73) by means of the low-temperature separation of air in a distillation column system, which distillation column system comprises a high-pressure column (21) and a low-pressure column (22). The entire 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 flow (8, 11, 14) of the feed air (7) compressed in the main air compressor (2) is cooled in a main heat exchanger (13) to an intermediate temperature and expanded in a first air turbine (15) in such a way that work is performed and is introduced into the distillation column system (40; 18, 19, 20). A second partial flow (12, 27, 29, 30) of the feed air compressed in the main air compressor (2) is post-compressed in a first post-compressor (9), cooled in the main heat exchanger (13), and then expanded (31) and introduced into the distillation column system. A first product flow (69; 75) is removed from the distillation column system in the liquid state, subjected to a pressure increase (71; 76) to a first product pressure, evaporated or pseudo-evaporated and heated in the main heat exchanger (13), and obtained as a first compressed-gas product (GOX IC; GAN IC). The entire feed air is compressed in a multi-stage main air compressor (2) from an inlet pressure to a final pressure. At least at times, a part (65) of the first partial flow (16) of the feed air expanded in such a way that work is performed is mixed with the total air flow downstream of the first stage of the main air compressor (2). In a first operating mode, a first amount of first compressed-gas product is obtained, and, in a second operating mode, a second, smaller amount is obtained. In the first operating mode, a first amount of air (65, 66) expanded in such a way that work is performed, which first amount can also be zero, is compressed in the main air compressor (2), and, in the second operating mode, a second, larger amount is compressed in the main air compressor.