Cryogenic Air Separation Heat Exchanger Layout for Lower Irreversibility
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Solution Overview
Problem
The existing air separation processes for industrial gases like oxygen, nitrogen, and argon are energy-intensive due to high irreversibilities in the cold section of the heat exchanger, leading to inefficient liquefaction and compression energy usage.
Innovation Solution
The process involves cooling compressed and purified air, warming gaseous nitrogen streams, vaporizing and liquefying oxygen or nitrogen streams, and expanding vaporized streams in a turbine to reduce irreversibilities in the heat exchanger, optimizing the energy efficiency by recycling high-pressure air streams and using a brazed aluminum plate fin heat exchanger.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional air separation processes are used with traditional heat exchanger configurations, then the separation of industrial gases can be achieved, but high irreversibilities in the cold section lead to excessive energy consumption
Solution Approach 1:
The heat exchanger is divided into a warm section and a cold section, with further segmentation into multiple channels (first, second, third channels) with different functions. The cold section is specifically segmented to optimize heat recovery, with streams arranged to minimize temperature differences and irreversibilities. This segmentation allows different parts of the system to be optimized for different purposes, reducing overall energy loss.
Solution Approach 2:
The patent inverts the traditional heat exchanger configuration by placing the cold section at the inlet end rather than the outlet end. This inversion allows the coldest streams to be introduced first, where they can be efficiently warmed by the warmest incoming streams, maximizing heat recovery and minimizing irreversibilities throughout the heat exchanger length.
2Temperature
If the cold section of the heat exchanger is designed for efficient cooling, then liquefaction can be achieved, but irreversibilities increase leading to higher compression and liquefaction energy requirements
Solution Approach 1:
The patent applies preliminary cooling actions by pre-cooling the incoming air stream in the cold section before it reaches the distillation columns. The cold section is designed to perform initial cooling and liquefaction preparation, reducing the energy burden on subsequent compression and liquefaction stages. This preliminary action optimizes the thermodynamic state of the feed before separation.
Solution Approach 2:
The patent changes the temperature and pressure parameters of various streams through the heat exchanger by optimizing the arrangement and number of transfer units in different channels. By carefully controlling parameter changes along the heat exchanger length, the system achieves efficient cooling and liquefaction while minimizing irreversibilities and associated energy consumption.
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 reduces energy consumption by approximately 1% in the air separation unit (ASU) by minimizing irreversibilities in the cold section of the heat exchanger, enhancing overall process efficiency.
Implementation Method 1
Compressed and purified air is cooled at a first pressure in a heat exchanger and the cooled air is sent in gaseous form from the heat exchanger to a column system comprising at least one distillation column
Implementation Method 2
A gaseous nitrogen stream from the column system is warmed in the heat exchanger
Implementation Method 3
A liquid stream enriched in oxygen or nitrogen from the column system is vaporized and warmed in the heat exchanger
Implementation Method 4
A first gaseous stream having a nitrogen content at least that of air and at a higher pressure than the first pressure is cooled and liquefied or pseudo liquefied in the heat exchanger to form a liquefied stream
Implementation Method 5
The vaporized stream is expanded, at least in part, in a turbine to form an expanded stream
Data Source
AI summary
An apparatus for the separation of air by cryogenic distillation comprises a column system, a heat exchanger, a turbine, means for sending compressed and purified air at a first pressure to be cooled at the first pressure in the heat exchanger, means for sending a first gaseous stream having a nitrogen content at least that of air to be cooled and liquefied or pseudo liquefied in the heat exchanger to form a liquefied stream, means for sending at least part of the liquefied stream to be warmed and vaporized in the heat exchanger to a first intermediate temperature of the heat exchanger to form a vaporized stream, means for removing the vaporized stream from an intermediate section of the heat exchanger, a conduit for sending the vaporized stream to be expanded, in the turbine to form an expanded stream, a conduit for sending at least part of the expanded stream to the column system, a conduit for sending a second gaseous stream having the same nitrogen content as the first stream to be cooled in the heat exchanger, means for removing at least part of the second gaseous stream from an intermediate section of the heat exchanger at a second intermediate temperature and sending the second gaseous stream to the turbine to be expanded with the vaporized stream.