Catalyst Mixing in FCC Regenerator Vessels
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Solution Overview
Problem
In fluid catalytic cracking (FCC) processes, incomplete combustion and nitrous oxide (NOx) emissions are issues due to uneven catalyst and combustion gas distribution in regenerators, leading to temperature differentials, equipment damage, and environmental concerns.
Innovation Solution
The process involves mixing spent and recycled regenerated catalysts in a confined volume within the regenerator vessel to maintain uniform temperatures, followed by oxygen contact to combust coke deposits, ensuring complete regeneration and minimizing NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If spent catalyst is not evenly distributed in the regenerator vessel, then catalyst mixing efficiency is reduced, but temperature differentials and hot spots increase causing equipment damage
Solution Approach 1:
The regenerator vessel is divided into multiple zones with different catalyst injection points and combustion air distribution zones. Catalyst is injected at multiple locations (e.g., wall injectors at different heights, central injector) to segment the distribution process, ensuring more uniform catalyst dispersion throughout the vessel and preventing hot spots.
Solution Approach 2:
Different regions of the regenerator vessel are provided with different characteristics: wall injectors provide catalyst at the periphery while a central injector provides catalyst at the core. Combustion air is distributed through multiple zones with different aeration levels, creating local quality variations that promote uniform overall distribution and prevent localized overheating.
2Object-generated harmful factors
If low excess air is used in the regenerator, then NOx emissions are reduced, but incomplete combustion occurs leading to after burn
Solution Approach 1:
The combustion process is segmented into multiple zones with progressively increasing excess air ratios. The first zone uses low excess air (0.5-2.0%) to minimize NOx formation during the primary combustion phase. Subsequent zones introduce additional air (second zone: 2-5%, third zone: 5-10%) to complete combustion of remaining CO and hydrocarbons, preventing after burn while maintaining low overall NOx emissions.
Solution Approach 2:
Catalyst is pre-distributed and pre-heated in the first combustion zone with controlled low excess air before entering subsequent zones. This preliminary combustion action reduces the carbon load on downstream zones, allowing complete combustion to occur at lower excess air levels in later zones, thereby preventing after burn while controlling NOx.
3Reliability
If CO promoter is added to promote complete combustion, then after burn is reduced, but NOx emissions increase
Solution Approach 1:
The function of the CO promoter is extracted and replaced by the multi-zone combustion system with progressive air introduction. Instead of relying on platinum or other precious metal promoters that increase NOx, the system uses hydraulic and aerodynamic design (multiple injectors, staged air injection) to achieve complete combustion without additional NOx-forming reactions.
Solution Approach 2:
The excess air ratio parameter is changed progressively through multiple zones rather than using a single high excess air level. This parameter progression (0.5-2.0% → 2-5% → 5-10%) enables complete combustion similar to CO-promoted systems but avoids the thermal conditions that generate high NOx emissions associated with single-stage high-excess-air combustion.
4Productivity
If multiple catalyst injectors are used to improve distribution, then equipment complexity increases, but mixing efficiency improves
Solution Approach 1:
The multiple injector system serves multiple functions simultaneously: catalyst distribution, catalyst pre-heating, and flow pattern control. The same wall injectors that distribute catalyst also create turbulent mixing and prevent dead zones, while the central injector provides both distribution and anchoring of the fluidized bed, reducing the need for separate dedicated components.
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 promotes uniform temperatures, reduces NOx production, and enhances catalyst activity, leading to more efficient coke combustion and lower equipment damage risks.
Implementation Method 1
Oxygen is contacted with spent catalyst to combust coke deposits from the spent catalyst to produce regenerated catalyst and flue gas
Implementation Method 2
combust coke deposits from the spent catalyst
Implementation Method 3
mixing spent and recycled regenerated catalysts in a confined volume within the regenerator vessel to maintain uniform temperatures
Implementation Method 4
Fluidization of the catalyst particles by various gaseous streams allows the transport of catalyst between the reaction zone and regeneration zone
Data Source
AI summary
Disclosed is a catalyst distributor and process for mixing spent catalyst and recycled regenerated catalyst in a regenerator vessel. Mixing is conducted in a confined space to which catalyst is delivered from catalyst conduits protruding through the wall of the regenerator.