FCC Waste Gas CO2 Separation by Adsorption and Cryogenic Distillation
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Solution Overview
Problem
Fluid bed catalytic cracking processes face challenges in efficiently separating carbon dioxide from waste gases due to high energy consumption and operational complexities in existing CO2 capture methods, particularly in oxycombustion modes, which are not yet established on an industrial scale.
Innovation Solution
A process that converts carbon monoxide in waste gases to carbon dioxide and uses adsorption and separation techniques, including pressure swing adsorption and partial condensation/distillation, to concentrate CO2 while minimizing nitrogen levels, without significant modifications to the core FCC process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If amine scrubbing is used to remove CO2 from waste gas, then CO2 capture efficiency is improved, but steam consumption increases significantly
Solution Approach 1:
The invention changes the temperature parameter of the waste gas from high temperature (500-850°C) to low temperature (below 0°C, preferably -30°C to -100°C) through expansion in a turbine or valve, enabling separation by partial condensation and distillation which consume less steam than amine scrubbing
Solution Approach 2:
The invention utilizes phase transition of CO2 from gas to liquid through cooling and compression, achieving separation by partial condensation and distillation. The CO2 is liquefied at temperatures below 0°C and pressures above atmospheric pressure, then separated from nitrogen through distillation
2Measurement precision
If oxycombustion mode is implemented to increase CO2 concentration, then CO2 purity in waste gas is improved, but operational stability deteriorates due to lack of industrial establishment
Solution Approach 1:
The invention applies partial oxycombustion by injecting oxygen-enriched air (20-40% oxygen) rather than pure oxygen, achieving sufficient CO2 concentration (50-70%) while maintaining better operational stability and avoiding the complete process modification required by full oxycombustion
Solution Approach 2:
The invention uses an intermediary separation process (low temperature condensation and distillation) between the regenerator and final CO2 product, allowing the use of moderately concentrated waste gas (50-70% CO2) from modified air combustion rather than requiring highly concentrated gas from full oxycombustion
3Stress or pressure
If waste gas is expanded to atmospheric pressure before CO2 removal, then pressure conditions are improved for downstream processing, but CO2 concentration decreases due to dilution
Solution Approach 1:
The invention changes the temperature parameter (cooling to below 0°C) and pressure parameter (compressing to 2-10 bar) of the expanded waste gas to enable efficient CO2 separation by partial condensation and distillation, compensating for the concentration decrease after expansion
Solution Approach 2:
The invention uses phase transition of CO2 to liquid state through compression and cooling after expansion, separating CO2 from nitrogen based on differences in condensation temperatures and distillation properties, thereby recovering CO2 even at lower concentrations
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 effectively reduces CO2 concentration in waste gases to between 60-70% and achieves efficient energy recovery, reducing the need for excess steam and fossil fuels, while maintaining stable operational conditions.
Implementation Method 1
i) if appropriate, at least a portion of the carbon monoxide of the waste gas is converted into carbon dioxide to form a flow enriched in carbon dioxide
Implementation Method 2
ii) the waste gas, or where applicable, the flow enriched in carbon dioxide from step i), is separated by adsorption to form a gas enriched in carbon dioxide and depleted in nitrogen
Implementation Method 3
iii) at least a portion of the gas enriched in carbon dioxide and depleted in nitrogen is separated in a separation device by way of separation at a temperature of less than 0° C. by partial condensation and/or by distillation to form a fluid rich in carbon dioxide
Implementation Method 4
iii) at least a portion of the gas enriched in carbon dioxide and depleted in nitrogen is separated in a separation device by way of separation at a temperature of less than 0° C. by partial condensation and/or by distillation to form a fluid rich in carbon dioxide
Data Source
AI summary
In a process for separating carbon dioxide from a waste gas (3) of a fluid bed catalytic cracking installation (1) containing carbon dioxide, nitrogen and possibly carbon monoxide, the waste gas (3) is separated by adsorption to form a gas enriched in carbon dioxide and depleted in nitrogen (29) and a gas rich in nitrogen and depleted in carbon dioxide (31), and at least a portion of the gas enriched in carbon dioxide and depleted in nitrogen is separated in a separation device (30) by way of separation at a temperature of less than 0° C. by partial condensation and/or by distillation to form a fluid rich in carbon dioxide (35) and a fluid depleted in carbon dioxide (37).