Multistage Cracking and Stripping in FCC Units
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Solution Overview
Problem
Current fluidized bed catalytic cracking (FCC) processes face inefficiencies in separating hydrocarbons from catalyst grains, leading to increased combustion, unwanted dry gases, and reduced production of high-value olefins and gas oil distillates, due to suboptimal stripping techniques.
Innovation Solution
A multi-stage cracking and stripping process is introduced, involving pre-stripping of catalyst grains and multiple cracking and stripping stages with structured packing elements, allowing for efficient hydrocarbon recycling and optimized catalyst regeneration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If single-stage stripping is used to separate hydrocarbons from catalyst grains, then the stripping operation is simpler, but hydrocarbon separation efficiency is insufficient leading to increased combustion and dry gas production
Solution Approach 1:
The stripping operation is divided into multiple stages: a first stripping stage using inert gas to remove light hydrocarbons, followed by a second stripping stage using steam to remove heavier hydrocarbons. This segmentation allows each stage to target specific hydrocarbon fractions, improving overall separation efficiency while managing the complexity through structured process design.
Solution Approach 2:
The first stripping stage using inert gas is performed as a preliminary action before the second steam stripping stage. This preliminary stripping removes light hydrocarbons and prepares the catalyst grains for more effective heavy hydrocarbon removal in the second stage, optimizing the sequence of operations to achieve better overall efficiency.
2Productivity
If extended stripping time is used to improve hydrocarbon removal, then separation efficiency increases, but catalyst deactivation accelerates due to excessive coking
Solution Approach 1:
The stripping process is segmented into two distinct stages with different durations and conditions. The first inert gas stripping stage is shorter and targets light hydrocarbons, while the second steam stripping stage is optimized for heavy hydrocarbon removal. This segmentation prevents excessive total stripping time that would cause catalyst deactivation while maintaining high removal efficiency for each hydrocarbon fraction.
Solution Approach 2:
The stripping process changes parameters between stages: the first stage uses inert gas at specific temperature and flow conditions optimized for light hydrocarbons, then transitions to the second stage using steam with different temperature and humidity parameters optimized for heavy hydrocarbons. These parameter changes enable efficient hydrocarbon removal at each stage without requiring excessive total processing time that would deactivate the catalyst.
3Object-generated harmful factors
If insufficient stripping is performed to maintain simple operations, then process complexity remains low, but combustion in regenerator increases producing unwanted dry gases
Solution Approach 1:
The stripping unit is segmented into two functional stages: the first stage using inert gas to remove light hydrocarbons that would otherwise contribute to combustion, and the second stage using steam to remove heavy hydrocarbons. This segmentation ensures thorough hydrocarbon removal before regenerator combustion, minimizing dry gas production while maintaining a structured but manageable process complexity.
Solution Approach 2:
The two-stage stripping process acts as an intermediary between the reactor and regenerator, removing hydrocarbons in controlled stages before the catalyst enters the regenerator. This intermediary stripping operation prevents excessive hydrocarbon combustion in the regenerator, reducing harmful byproducts while the structured two-stage approach manages overall process complexity.
4Productivity
If multiple cracking stages are implemented to maximize olefin production, then olefin yield increases, but process complexity and thermal balance control become more difficult
Solution Approach 1:
The cracking process is segmented into multiple stages with distinct functions: the first cracking stage in the reactor produces initial olefins and gasoline, while subsequent cracking stages in the stripping unit further convert gasoline to additional olefins. Each stage is optimized for specific conversion objectives, maximizing overall olefin yield while the segmented structure allows independent optimization of each stage's conditions.
Solution Approach 2:
The stripping unit is given multi-functionality: it serves both as a hydrocarbon removal device and as an additional cracking reactor. By implementing cracking functionality within the existing stripping unit structure, the process achieves multiple cracking stages without proportionally increasing overall device complexity, as the same equipment performs dual functions.
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 production of high-value olefins and distillates while maintaining thermal balances, reducing coke and dry gas production, and extending catalyst life by improving catalyst activity and hydrocarbon conversion efficiency.
Implementation Method 1
the grain stripping takes place will be called the stripper
Implementation Method 2
an inert gas, preferably steam, which removes any traces of residual hydrocarbons trapped in the pores of each catalyst grain
Implementation Method 3
The portion of the disengager/striper that separates the grains from the hydrocarbons by ballistic or centrifugal separation
Implementation Method 4
The portion of the disengager/striper that separates the grains from the hydrocarbons by ballistic or centrifugal separation
Implementation Method 5
the feedstock is injected into a main reactor where it is contacted with hot catalyst grains in a fluidized bed
Implementation Method 6
contacted with hot catalyst grains in a fluidized bed
Implementation Method 7
which come from the regenerator, which is responsible for burning off the coke deposited on the catalyst grains during the feedstock cracking under an oxidizing atmosphere
Implementation Method 8
burning off the coke deposited on the catalyst grains during the feedstock cracking under an oxidizing atmosphere
Data Source
Figure 1A~1C
Figure 2~4
Figure 5a~5c
AI summary
The present invention relates to a multistage cracking and stripping process that can be used in a fluidized-bed catalytic cracking process or FCC (fluidized catalytic cracking) process for maximizing the production of olefins, that is to say of C3 and C4 olefins, in particular propylene and distillates. One subject of the present invention is therefore a multistage process for cracking and stripping a fluidized mixture of hydrocarbons and of coked catalyst particles, integrated into a conventional fluidized-bed catalytic cracking process, comprising at least one cracking step and one stripping step after separation of the coked catalyst particles and of the effluents cracked during the disengaging/stripping step, characterized in that it comprises at least two steps of cracking at least one hydrocarbon-based fluid over the separated coked catalyst particles, followed by at least two steps of stripping these particles, each cracking step preceding a stripping step. The present invention also relates to a separating and stripping device that implements this process.