FCC Plenum Baffle for Coke Mitigation
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Solution Overview
Problem
In the FCC process, severe coking occurs in the plenum of the reactor vessel due to incomplete cracking of oil feed into vapor products, leading to loss of vapor product and requiring extensive maintenance, which can cause mechanical integrity issues between the plenum and the top head of the reactor vessel.
Innovation Solution
A baffle is introduced in the plenum to create an inner volume for product vapors, minimizing their contact with the cool plenum and reducing the time they spend there, thereby limiting coke formation and preventing entry into low fluidization zones, while a purge gas is used to further isolate and purge these zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If product vapors are discharged directly into the plenum, then the plenum can collect and discharge gases efficiently, but severe coking occurs in the plenum due to contact between hot vapors and cool plenum surfaces
Solution Approach 1:
The plenum is segmented into an inner volume and an outer volume by a baffle. The inner volume receives hot product vapors from cyclones, while the outer volume contains cool purge gas. This segmentation prevents direct contact between hot vapors and cool plenum surfaces, eliminating coking while maintaining gas discharge efficiency.
Solution Approach 2:
The baffle acts as an intermediary structure that physically separates the inner and outer volumes. It directs hot vapors into the inner volume and prevents them from contacting the cool outer plenum surfaces, thereby preventing coke formation while allowing efficient gas collection and discharge.
2Ease of operation
If the plenum volume is large to accommodate gas conduits and allow gas collection, then gas discharge is facilitated, but low fluidization zones are created where catalyst can become entrained with product gases
Solution Approach 1:
The plenum is divided into an inner volume for hot vapors and an outer volume for cool purge gas and catalyst bed. This segmentation creates distinct functional zones that prevent catalyst entrainment in product gases while maintaining effective gas collection and discharge capabilities.
Solution Approach 2:
Purge gas is introduced into the outer volume to create a fluidized bed that prevents catalyst particles from being entrained with product gases. The pneumatic action of purge gas maintains catalyst fluidization and separation, ensuring reliable product gas discharge without catalyst contamination.
3Productivity
If product vapors remain in the plenum for extended periods before discharge, then complete gas collection is achieved, but coke formation increases due to prolonged residence time
Solution Approach 1:
The segmented plenum design with inner and outer volumes allows hot product vapors to be quickly directed into the inner volume and discharged, minimizing residence time. The outer volume with purge gas prevents coking while the overall system maintains complete gas collection efficiency.
Solution Approach 2:
The baffle configuration and volume design enable hot vapors to quickly pass through the inner volume and be discharged, rather than lingering in the plenum. This rushing through approach minimizes residence time and coke formation while maintaining complete gas collection.
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 by minimizing the residence time of product vapors and preventing their entry into low fluidization zones, thereby reducing maintenance needs and preventing mechanical integrity issues.
Implementation Method 1
A baffle is introduced in the plenum to create an inner volume for product vapors, minimizing their contact with 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. In the operation of an FCC 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. The centripetal acceleration associated with an exterior of the vortex causes catalyst particles to migrate towards the outside of the barrel
Implementation Method 3
The heavier catalyst particles accumulate on the side wall of the cyclone barrel by centrifugal force and eventually drop to the bottom of the cyclone
Implementation Method 4
The catalyst bed is typically fluidized to facilitate entry of the catalyst into a stripper vessel. The reactor vessel contains a large volume of empty space in which catalyst can become entrained with gaseous product that has not yet exited the reactor vessel. Typically, the reactor vessel is purged with an inert gas, such as steam, to activate low fluidization zones
Data Source
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.