Catalytic Cracking Heat Balance via Coking Effluent Recycle
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Solution Overview
Problem
Catalytic cracking units face challenges in maintaining thermal balance when processing low-coking charges with high hydrogen content, leading to issues like afterburning and catalyst deactivation due to insufficient coke deposition and uneven combustion, which affects the operational efficiency and stability of the FCC process.
Innovation Solution
A process that involves recycling a coking hydrocarbon effluent rich in aromatic compounds onto the catalyst before regeneration, adjusting the quantity of coke on the catalyst to ensure sufficient heat balance and temperature, while using structured packing elements in the stripper to homogenize catalyst distribution and prevent hot spots, thereby maintaining catalyst activity and achieving thermal equilibrium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a low-coking charge with high hydrogen content is processed in an FCC unit, then the product yield and quality are improved, but the thermal balance of the unit cannot be maintained due to insufficient coke deposition
Solution Approach 1:
The patent introduces a preliminary coking step before the main catalytic cracking reaction. A coking cut (heavy hydrocarbon fraction) is recycled and contacted with the fresh feed in a coking reactor to pre-deposit coke on the catalyst. This preliminary action ensures sufficient coke is available for combustion in the regenerator, maintaining thermal balance even when processing low-coking charges with high hydrogen content.
2Temperature
If air flow is increased to improve combustion and heat balance, then the temperature of regenerated catalyst increases, but CO content in flue gases increases and thermal efficiency decreases
Solution Approach 1:
The patent changes the composition and quantity parameters of the coke feedstock by recycling a specific coking cut with controlled properties (high aromatic content, specific Conradson carbon value). By controlling the flow rate and composition of the recycled coking cut, the system optimizes the amount and quality of coke deposited, ensuring complete combustion at lower air flow rates, maintaining catalyst temperature while improving thermal efficiency and reducing CO emissions.
3Use of energy by moving object
If a coking cut is recycled to increase coke deposition, then the heat balance is improved, but afterburning and hot spots occur in the regenerator causing catalyst deactivation
Solution Approach 1:
The patent divides the coking process into two separate stages: (1) a coking reaction stage in a dedicated coking reactor where coke is gradually deposited on catalyst under controlled conditions, and (2) a combustion stage in the regenerator. This segmentation prevents rapid, uncontrolled combustion of large amounts of coke, avoiding afterburning and hot spots that would deactivate the catalyst, while still achieving sufficient heat balance through controlled coke combustion.
Solution Approach 2:
The coking cut is pre-contacted with fresh feed in a coking reactor to gradually deposit coke on catalyst particles before they enter the regenerator. This preliminary, controlled coke deposition ensures uniform coke distribution and prevents sudden, violent combustion in the regenerator, thereby avoiding afterburning and protecting catalyst integrity while maintaining heat balance.
4Use of energy by moving object
If the quantity of coking cut recycled is increased to ensure heat balance, then coke deposition is sufficient, but the complexity of the process increases and operational stability decreases
Solution Approach 1:
The patent makes the coking cut serve multiple functions simultaneously: (1) it acts as a feedstock for coke deposition, (2) it serves as a heat source for maintaining regenerator temperature, (3) it provides process flexibility for handling different feed types, and (4) it enables continuous operation during feed changes. This multi-functionality reduces the need for separate systems and simplifies overall process operation while ensuring heat balance.
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 increases the coke deposition on catalysts, ensuring complete combustion and maintaining the desired temperature in the regenerator, thus preventing afterburning and deactivation, and ensuring the proper functioning of the catalytic cracking unit even with weakly coking charges.
Implementation Method 1
the combustion of the coke deposited on the catalyst during the reaction step. This combustion takes place in the regeneration zone
Implementation Method 2
making it possible to increase the quantity of coke on the catalyst before its entry into the regenerator operating in combustion mode, but also making it possible to avoid the formation of hot spots in the diluted phase of the fluidized bed
Data Source
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AI summary
The invention relates to a method for the catalytic cracking, using a fluidized bed, of a slightly coking Conradson carbon feedstock of no more than 0.1 wt % and having a hydrogen content of no less than 12.7 wt %, said method including: at least one step of cracking for the feedstock; a step for separating/stripping the effluents of the coked catalyst grains; and a step of regenerating said grains. The method is characterized in that at least one so-called coking carbon or hydrocarbon effluent, having an aromatic-compound content of more than 50 wt % and including more than 20 wt % of polyaromatic compounds, is recirculated over the homogeneously-distributed slightly-coking catalyst before regeneration in order to adjust the delta coke of the method.