Two-Layer Adsorbent System for Cryogenic Air Pre-Purification
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Solution Overview
Problem
Current air pre-purification methods for cryogenic air separation struggle with efficient removal of water, carbon dioxide, nitrous oxide, and hydrocarbons, leading to operational issues like pressure drops, flow variations, and safety hazards due to their freezing and explosive potential, and existing adsorption processes are energy-intensive or require frequent depressurization, resulting in high costs and plant instability.
Innovation Solution
A process utilizing a two-layer adsorbent system where activated alumina with high water capacity is used upstream, followed by a second adsorbent with balanced Henry's Law selectivity for CO2 and N2O, allowing simultaneous breakthrough of CO2 and N2O, and using a low-temperature regeneration to minimize energy consumption and prevent nitrous oxide displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pressure swing adsorption (PSA) is used for pre-purification, then the removal of water and carbon dioxide is effective, but frequent depressurization is required leading to high switch loss and feed gas venting
Solution Approach 1:
The patent changes the operating parameters by using a much longer cycle time (2-12 hours vs 10-15 minutes) and allowing the heat pulse to exit the bed during the feed period. This parameter change transforms the process from frequent PSA cycles to extended TSA cycles, reducing the frequency of depressurization events and associated switch losses.
Solution Approach 2:
The patent implements periodic regeneration with extended feed times of 2-12 hours, allowing the adsorption process to run for much longer periods before regeneration is required. This periodic action with extended duration reduces the number of depressurization cycles needed.
2Duration of action of moving object
If thermal swing adsorption (TSA) is used for pre-purification, then the cycle time is extended, but high regeneration temperatures (150-200°C) are required increasing energy consumption
Solution Approach 1:
The patent changes the temperature parameter by using lower regeneration temperatures (50-150°C vs 150-200°C) while maintaining extended cycle times. This parameter optimization reduces the energy input required for heating the regenerating gas while still achieving effective desorption of adsorbed components.
3Device complexity
If a single adsorbent bed is used for CO2 removal, then the process is simple, but nitrous oxide breaks through ahead of CO2 causing operational problems
Solution Approach 1:
The patent segments the adsorbent bed into two distinct functional zones: an upstream zone (70-90% of bed volume) optimized for CO2 adsorption, and a downstream zone (10-30% of bed volume) optimized for N2O adsorption. This segmentation allows each zone to perform its specific function effectively, preventing N2O breakthrough while maintaining reasonable process complexity.
Solution Approach 2:
The patent applies local quality by using different adsorbent materials with different selectivity characteristics in different parts of the bed. The upstream zone uses an adsorbent with high CO2 selectivity, while the downstream zone uses an adsorbent with high N2O selectivity, ensuring that each location in the bed has the appropriate properties for its specific function.
4Productivity
If adsorption is run indefinitely, then the mass transfer zone moves downstream, but eventually components break through requiring regeneration
Solution Approach 1:
The patent uses CO2 breakthrough monitoring as a feedback signal to trigger regeneration. By monitoring CO2 levels in the effluent stream and using this information to determine when regeneration is needed, the system maintains continuous operation while preventing N2O breakthrough. The feedback mechanism allows the system to operate at optimal capacity without sacrificing reliability.
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
Effectively reduces water, carbon dioxide, and nitrous oxide levels below desired thresholds, minimizing hydrocarbon breakthrough and energy usage, while maintaining operational stability and safety by ensuring simultaneous CO2 and N2O breakthrough, thus preventing downstream hazards and reducing plant costs.
Implementation Method 1
passing said feed air stream at a feed temperature and a feed pressure in a feed direction through a first adsorbent, whose Henry's Law selectivity for CO2 over N2O measured at 30°C is at least 12.5
Implementation Method 2
subsequently through a second adsorbent, whose Henry's Law constant for the adsorption of CO2 measured at 30°C is less than 1020 mmol/g/atm and whose Henry's Law selectivity for CO2 over N2O measured at 30°C is at most 5
Implementation Method 3
passing a heated regenerating gas at the second pressure and at a temperature which is between 20°C and 80°C to at least the second adsorbent in a direction opposite to the feed direction
Implementation Method 4
passing a second regenerating gas at the second pressure and at a temperature less than the temperature of the heated regenerating gas to the first and second adsorbents in a direction opposite to the feed direction
Data Source
AI summary
Reduction of water, CO2 and N2O in an air stream comprising: passing said air stream at a feed temperature through a first adsorbent, whose Henry's Law selectivity for CO2/N2O is at least 12.5, and a second adsorbent, whose Henry's Law constant for CO2 is less than 1020 mmol/g/atom and whose Henry's Law selectivity for CO2/N2O is at most 5; and passing a heated regenerating gas at a temperature which is between 20° C. and 80° C. to at least the second adsorbent, and passing a second regenerating gas at a temperature less than the temperature of the heated regenerating gas to the first and second adsorbents in a direction opposite to the feed direction; the second adsorbent occupying from 25% to 40% of the total volume of the adsorbents, and the temperature of the heated regenerating gas being 10° C. to 60° C. higher than the feed temperature.