Counter-Current Regenerator Riser Mitigating 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, featuring permeable barriers that allow downward catalyst flow and upward oxygen-containing gas flow, mitigating backmixing and promoting efficient coke combustion by achieving true counter-current contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional bubbling bed regenerator is used with single dense catalyst bed, then catalyst regeneration can be achieved, but back mixing occurs causing non-uniform combustion, hot spots, and increased equipment size
Solution Approach 1:
The regenerator is divided into multiple stages (first stage, second stage, third stage) with distinct functions. The first stage performs primary combustion with air injection, the second stage completes combustion and removes remaining carbon monoxide, and the third stage serves as a transition zone. This segmentation eliminates back mixing by creating unidirectional flow paths and prevents hot spots by distributing combustion across stages.
Solution Approach 2:
The invention introduces a vertical dimension to catalyst flow by using a regenerator riser that transports catalyst upward from the dense bed to the dilute phase zone. This vertical transport creates true counter-current contact between downward-flowing catalyst and upward-flowing gas, replacing the horizontal back-mixing pattern of conventional bubbling beds.
2Reliability
If two-stage bubbling bed regenerator is used to finish catalyst clean up, then carbon on catalyst is reduced to minimum, but residence time increases and combustion rate becomes non-uniform
Solution Approach 1:
The invention creates dynamic flow patterns by introducing a regenerator riser that actively transports catalyst upward using gas lift, rather than relying on passive settling. This dynamic transport mechanism controls residence time by adjusting gas flow rates, ensuring uniform combustion while maintaining complete carbon removal through the multi-stage counter-current contact.
3Ease of operation
If catalyst is lifted upward by air distributed into regenerator, then catalyst is transported, but back mixing occurs from top to bottom reducing bed density
Solution Approach 1:
The invention inverts the conventional approach by having catalyst fall downward through the regenerator stages under gravity while gas flows upward, rather than lifting catalyst upward through the entire bed. The regenerator riser provides the necessary upward transport, but the main regeneration zones experience downward catalyst flow, eliminating back mixing and maintaining high bed density.
4Use of energy by moving object
If high carbon monoxide concentration is maintained in flue gas for heat recovery, then heat recovery efficiency increases, but after burn risk increases due to insufficient oxygen
Solution Approach 1:
The invention performs preliminary combustion in the first stage with sufficient oxygen supply, converting most carbon to carbon dioxide before the flue gas enters the heat recovery system. The second stage then completes any remaining combustion in a controlled manner, preventing after burn in downstream equipment while maintaining high heat recovery efficiency from the CO2-rich flue gas.
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 ensures uniform catalyst residence time, reduces equipment size, and enhances combustion efficiency, preventing afterburn while minimizing oxygen requirements and 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
Implementation Method 2
The regenerator riser may provide a passage to transport the catalyst
Implementation Method 3
In the regenerator, the coke is burned from the catalyst with oxygen-containing gas, usually air
Implementation Method 4
combusts coke from the catalyst
Implementation Method 5
counter-current contact along with a regenerator riser
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.