Direct Feed-Effluent Heat Exchange in FCC Main Column
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Solution Overview
Problem
Fluid catalytic cracking (FCC) processes face challenges with high coke production due to feeds containing coke precursors, leading to reduced catalyst activity and poorer product quality, especially when processing heavier hydrocarbon feeds.
Innovation Solution
Implementing direct reactor feed/reactor effluent heat exchange in the FCC main column, utilizing hydroprocessed hydrocarbon feeds with reduced coke precursors, which allows for optimized thermal efficiency and catalyst regeneration with an oxygen-rich gas stream, minimizing net production of high boiling hydrocarbons and reducing catalyst coke generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional FCC processes use heavier hydrocarbon feeds, then feedstock versatility is improved, but coke production increases and catalyst activity decreases
Solution Approach 1:
The patent applies preliminary action by hydroprocessing the feedstock before FCC to remove coke precursors (conradson carbon residue, asphaltenes, heteroatomic compounds) in advance. This pre-treatment prevents coke formation during cracking, allowing heavier feeds to be processed without the usual coke production problems.
Solution Approach 2:
The patent changes the chemical composition parameters of the feedstock through hydroprocessing, reducing conradson carbon residue to less than 2% and asphaltenes to less than 0.5%. These parameter changes enable heavier feeds to be cracked with low coke yield, resolving the contradiction between feed versatility and coke production.
2Use of energy by moving object
If direct reactor feed/reactor effluent heat exchange is implemented, then thermal efficiency is improved, but temperature control complexity increases
Solution Approach 1:
The patent merges the heat exchange function into the existing FCC main column by implementing a direct heat exchange section where reactor effluent contacts reactor feed. This integration combines heating and cooling functions in a single unit, improving thermal efficiency without proportionally increasing device complexity.
Solution Approach 2:
The reactor effluent serves dual purposes: it is cooled to recover heat while simultaneously serving as a heating medium for the reactor feed. This self-service arrangement improves thermal efficiency by utilizing the temperature difference between effluent and feed without requiring external utilities.
3Productivity
If oxygen-rich regeneration gas is used, then catalyst regeneration efficiency is improved, but safety risks increase
Solution Approach 1:
The patent changes the oxygen concentration parameter in the regeneration gas from conventional levels (21% in air) to oxygen-rich levels (greater than 30%, preferably greater than 50%). This parameter change accelerates coke combustion and improves regeneration efficiency, with safety managed through controlled injection rates and distribution.
Solution Approach 2:
The patent uses oxygen-rich gas as a strong oxidant to accelerate coke combustion on the catalyst surface. The higher oxygen concentration provides more oxygen molecules per unit volume, intensifying the oxidation reaction and improving regeneration efficiency while maintaining safety through proper engineering controls.
4Object-generated harmful factors
If hydroprocessed hydrocarbon feeds are used, then coke precursors are reduced, but processing cost increases
Solution Approach 1:
The patent applies preliminary hydroprocessing action to remove coke precursors before FCC. While this adds a processing step, it enables the use of heavier, more valuable feedstocks that would otherwise be difficult to crack, potentially offsetting the additional processing cost through improved feedstock utilization and product yield.
Solution Approach 2:
The patent changes the chemical parameters of the feedstock (conradson carbon residue, asphaltenes, heteroatomic compounds) through hydroprocessing to achieve low coke production in FCC. This parameter transformation enables heavier feeds to be processed economically with improved catalyst life and reduced regeneration costs.
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 the yield of desired products like gasoline boiling range hydrocarbons, reduces coke yield, and improves catalyst regeneration efficiency, resulting in lower utility requirements and higher quality FCC products.
Implementation Method 1
Direct FCC reactor feed/reactor effluent heat exchange optimizes thermal efficiency and may be conveniently carried out in the main fractionating column
Implementation Method 2
the coke is removed by combustion with an oxygen-containing regeneration gas
Implementation Method 3
contacting such feeds with hydrogen in the presence of a suitable hydroprocessing catalyst
Data Source
AI summary
Fluid catalytic cracking (FCC) processes are described, in which hydroprocessed hydrocarbon streams or other hydrocarbon feed streams having a low coking tendency are subjected to direct heat exchange with the FCC reactor effluent, for example in the FCC main column. The processes operate with sufficient severity such that little or no net FCC main column bottoms liquid (e.g., with a 343° C. (650° F.) distillation cut point) is generated. Regeneration temperatures with the representative low coking tendency feeds are beneficially increased by using an oxygen-enriched regeneration gas stream.