Cryogenic Air Distillation Staging for Lower Compression Heat
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Solution Overview
Problem
Current air separation processes for producing oxygen by vaporization of liquid oxygen face inefficiencies in energy usage due to insufficient cold-boosted air flow, limiting the reduction of compression heat in the heat exchanger.
Innovation Solution
A process involving multiple compression and cooling steps to generate a pressurized gas stream, where air is compressed in stages to different pressures, cooled, and then introduced into a heat exchanger to optimize energy efficiency by minimizing compression heat introduction, allowing for increased gaseous oxygen production and improved energy performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a portion of air is compressed in a cold booster and expanded in an expansion turbine, then the air available for expansion is sufficient, but the compression heat introduced into the heat exchanger increases energy consumption
Solution Approach 1:
The air flow is divided into three distinct portions: a first portion compressed in a hot booster, a second portion compressed in a cold booster and expanded in a turbine, and a third portion compressed only in the hot booster. This segmentation allows optimization of each portion's path to balance expansion requirements with energy efficiency.
Solution Approach 2:
Different portions of air are given different treatment paths based on local requirements. The second portion specifically routed through the cold booster and turbine receives localized quality enhancement (cold compression and expansion) to provide sufficient cold air flow for the turbine while minimizing overall compression heat in the heat exchanger.
2Use of energy by moving object
If the cold-boosted air flow is reduced to minimize compression heat, then energy efficiency improves, but the air available for the expansion turbine becomes insufficient
Solution Approach 1:
The air flow is segmented into multiple portions with different compression paths. The second portion is specifically allocated to the cold booster and turbine path, ensuring sufficient air flow for expansion while the first and third portions are optimized for energy efficiency in the hot booster path.
Solution Approach 2:
The second portion of air serves dual purposes: it is compressed in the cold booster and then expanded in the turbine, where it provides the necessary cold air flow for turbine operation. This self-service arrangement ensures the turbine receives adequate air flow without requiring excessive cold-boosted air that would increase overall compression heat.
3Productivity
If liquid oxygen is vaporized by heat exchange with compressed air, then gaseous oxygen is produced, but the compression heat reduces the vaporization efficiency
Solution Approach 1:
The compressed air is segmented into three portions with different compression paths. This segmentation allows the heat exchanger to receive air with optimized thermal characteristics, improving the vaporization efficiency of liquid oxygen while maintaining high oxygen production rates.
Solution Approach 2:
The compression parameters (pressure, temperature) of different air portions are changed and optimized for their specific functions. The third portion compressed only in the hot booster provides heat for vaporization, while the second portion provides cold flow for the turbine, optimizing overall energy utilization and vaporization efficiency.
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 method enhances energy efficiency by optimizing the air stream's pressure and temperature conditions, enabling more efficient vaporization of oxygen and reducing energy consumption in the air separation unit, thereby improving overall plant performance.
Implementation Method 1
all or part of the feed air flow is brought to a pressure P1, at least 5 bar greater than the pressure of the medium-pressure column, by means of a first compressor
Implementation Method 2
a portion of the air compressed in the first compressor undergoes an additional compression step starting from the temperature T1 and pressure P1 to a pressure P2 greater than P1, then is cooled, typically by heat exchange with water, to the temperature T2 where T2 and T1 differ by less than 10° C.
Implementation Method 3
this cooled portion is then introduced into a heat exchanger of an air separation unit in order to undergo cooling to a temperature below or equal to −100° C.
Implementation Method 4
at least 50%, preferably at least 70%, of the total air flow supplies, in gaseous form, at least one distillation column of the unit, after having been expanded in an expansion turbine
Implementation Method 5
air is separated in the system of columns
Implementation Method 6
this cooled portion is then introduced into a heat exchanger of an air separation unit in order to undergo cooling to a temperature below or equal to −100° C.
Implementation Method 7
liquid oxygen is drawn from one of the distillation columns, pressurized by means of a pump to the required pressure which is greater than 20 bar abs
Implementation Method 8
liquid oxygen is drawn from one of the distillation columns, pressurized by means of a pump to the required pressure which is greater than 20 bar abs, vaporized by heat exchange
Data Source
AI summary
Process for producing gaseous oxygen by cryogenic distillation of air, wherein a portion of the feed air flow is brought to a pressure P1, by means of a first compressor, the suction temperature T0 of which is between 0 and 50° C., the gas at the pressure P1 is cooled, in order to generate an air stream at the pressure P1 and the temperature T1 between 5 and 45° C., a portion of the air compressed in the first compressor undergoes an additional compression step starting from the temperature T1 and pressure P1 to a pressure P2 greater than P1, then is cooled, to the temperature T2 where T2 and T1 differ by less than 10° C.