Counter-Current Regenerator Riser Mitigates Catalyst Backmixing
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Solution Overview
Problem
Current catalyst regeneration processes in fluidized catalytic cracking units face inefficiencies due to afterburn and backmixing, leading to incomplete coke combustion, catalyst deactivation, and increased equipment size, which necessitates improved control over coke and oxygen concentration and temperature profiles.
Innovation Solution
A counter-current catalyst regenerator with multiple stages and a regenerator riser, utilizing permeable barriers to facilitate counter-current flow and prevent backmixing, allowing for more uniform catalyst residence time and efficient coke combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional bubbling bed regenerator is used with air bubbled through a dense catalyst bed, then the catalyst can be regenerated, but back mixing occurs causing non-uniform residence time and combustion rate, leading to hot spots and reduced combustion efficiency
Solution Approach 1:
The regenerator is divided into multiple stages (first stage, second stage, and optional third stage) with distinct functions. The first stage performs primary combustion with high oxygen concentration, the second stage completes combustion with lower oxygen concentration, and the third stage (if present) polishes remaining carbon monoxide. This segmentation eliminates back mixing by creating sequential processing zones with controlled catalyst flow and oxygen distribution, ensuring uniform residence time and combustion rate across stages.
2Use of energy by moving object
If the carbon monoxide concentration in flue gas is increased to maximize heat recovery, then heat recovery efficiency improves, but the risk of after burn and uncombusted coke on catalyst increases
Solution Approach 1:
The system performs preliminary complete combustion in the first and second stages before the flue gas exits the regenerator. By ensuring that carbon monoxide is fully converted to carbon dioxide in controlled stages with adequate oxygen supply and residence time, the flue gas leaving the regenerator has minimal unburnt carbon and low oxygen content, eliminating the after burn risk while maintaining high heat recovery efficiency in downstream equipment.
3Quantity of substance
If a two-stage bubbling bed regenerator is used to finish catalyst clean up, then carbon on catalyst is reduced to minimum, but the equipment size increases and operational complexity increases
Solution Approach 1:
Each stage is designed with specific local characteristics optimized for its function. The first stage has high oxygen concentration and aggressive combustion conditions for rapid coke removal. The second stage has lower oxygen concentration and milder conditions for completing combustion and polishing catalyst. The third stage (when present) provides final carbon monoxide oxidation. This local optimization allows each section to be compact while achieving complete regeneration, reducing overall equipment size compared to a single large-stage design.
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 enhances coke burn efficiency, reduces catalyst deactivation, and minimizes equipment size by achieving uniform coke and oxygen concentration profiles, thereby improving overall regenerator efficiency and reducing operational costs.
Implementation Method 1
Each stage may comprise a permeable barrier that allows upward passage of oxygen-containing gas and downward passage of coked catalyst into each stage, but inhibits upward movement of catalyst
Implementation Method 2
the coke is burned from the catalyst with oxygen-containing gas, usually air
Implementation Method 3
combusts coke from the catalyst
Implementation Method 4
counter-current contact between flue gas and regenerated catalyst
Data Source
AI summary
A counter-current catalyst regenerator with at least two stages of counter-current contact along with a regenerator riser is proposed. Each stage may comprise a permeable barrier that allows upward passage of oxygen-containing gas and downward passage of coked catalyst into each stage, but inhibits upward movement of catalyst to mitigate back mixing and approximate true counter-current contact and efficient combustion of coke from catalyst. The regenerator riser may provide a passage to transport the catalyst and may serve as a secondary stage for coke combustion to provide the regenerated catalyst.