FCC Plenum Baffle for Coke Mitigation
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Solution Overview
Problem
In the FCC process, severe coking occurs in the plenum of reactor vessels due to incomplete cracking of oil feeds, leading to vapor product loss and increased maintenance needs, which can cause mechanical integrity issues between the plenum and reactor vessel connections.
Innovation Solution
A baffle is used to create an inner volume within the plenum to prevent contact between hot product vapors and the cool plenum, minimizing coke formation and reducing the time spent in low fluidization zones by distributing a purge gas into an outer volume to purge gases from the outer volume, thereby reducing coke growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If product vapors are allowed to collect in the plenum for prolonged periods, then the plenum can accommodate the vapor volume, but severe coking occurs leading to vapor product loss and mechanical integrity issues
Solution Approach 1:
The plenum is segmented into an inner volume and an outer volume using a baffle. The inner volume receives hot product vapors from cyclones, while the outer volume contains cooling purge gas. This segmentation prevents direct contact between hot vapors and cool plenum walls, eliminating the temperature gradient that causes coking while maintaining adequate vapor accommodation volume.
Solution Approach 2:
A baffle acts as an intermediary structure between the hot product vapors and the cool plenum walls. It creates a thermal barrier that prevents heat transfer from vapors to walls, thereby preventing coke formation. The baffle also directs vapor flow through the inner volume to the discharge outlet, ensuring prolonged residence time without coking.
2Speed
If the plenum is purged with inert gas to activate low fluidization zones, then catalyst entry is quickened, but coke formation increases in the plenum
Solution Approach 1:
The plenum is divided into inner and outer volumes. The outer volume receives purge gas for activating low fluidization zones and quickening catalyst entry, while the inner volume contains hot product vapors. This segmentation isolates the vapor-containing inner volume from coke-forming conditions while allowing purge gas to perform its fluidization activation function in the outer volume.
Solution Approach 2:
Different regions of the plenum are given different functions: the outer volume is designated for purge gas introduction and low fluidization zone activation, while the inner volume is designated for hot vapor containment and discharge. This local differentiation allows purge gas to speed up catalyst entry without exposing vapors to cooling and coking conditions.
3Object-generated harmful factors
If a baffle is used to create an inner volume to prevent vapor-cool plenum contact, then coke formation is reduced, but device complexity increases
Solution Approach 1:
The baffle segments the plenum into two functional volumes using a single structural element. This simple segmentation approach effectively prevents vapor-wall contact and coke formation without requiring complex multi-component systems. The baffle's straightforward geometry minimizes manufacturing and installation complexity.
Solution Approach 2:
The baffle serves as a simple intermediary structure that accomplishes multiple functions: it prevents thermal contact between vapors and walls, directs vapor flow through the inner volume, and provides structural support for the volume segmentation. Its simplicity as a single element minimizes added device complexity while achieving the desired coke prevention.
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 solution significantly reduces coke deposits in the plenum, minimizing maintenance time and preventing mechanical integrity issues by shortening the residence time of product vapors and preventing coke precursors from entering low fluidization zones, achieving a reduction of 80-90% in dead zones behind gas conduits.
Implementation Method 1
A baffle is used to create an inner volume within the plenum to prevent contact between hot product vapors and the cool plenum
Implementation Method 2
Cyclones usually comprise an inlet that is tangential to the outside of a cylindrical vessel that forms an outer wall of the cyclone... the entry and the inner surface of the outer wall cooperate to create a spiral flow path of the gaseous materials and catalyst that establishes a vortex in the cyclone
Implementation Method 3
The centripetal acceleration associated with an exterior of the vortex causes catalyst particles to migrate towards the outside of the barrel while the gaseous materials enter an interior of the vortex... The heavier catalyst particles accumulate on the side wall of the cyclone barrel by centrifugal force
Implementation Method 4
distributing a purge gas into an outer volume in the plenum outside of the inner volume to purge gases from the outer volume
Implementation Method 5
The catalyst bed is typically fluidized to facilitate entry of the catalyst into a stripper vessel
Implementation Method 6
spent catalyst is conventionally transferred to a stripper that removes adsorbed and entrained hydrocarbon gases from catalyst and then to a regenerator for purposes of removing the coke by oxidation with an oxygen-containing gas. Oxidizing the coke from the catalyst surface releases a large amount of heat
Data Source
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AI summary
An apparatus and process is disclosed for mitigating coking in an FCC reactor plenum. The apparatus and process utilize a baffle to create a inner volume for the product vapors to prevent contact with a relatively cool plenum. The baffle also limits the amount of the time the product vapors spend in the plenum minimizing time for coke formation and limit product vapors from entering low fluidization zones.