FCC Regenerator Catalyst Recirculation for NOx Reduction
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Solution Overview
Problem
Current fluid catalytic cracking (FCC) regenerators face challenges in minimizing nitrogen oxide (NOx) emissions while ensuring complete catalyst regeneration, particularly due to the use of platinum-based CO combustion promoters and excess oxygen, which increase NOx production.
Innovation Solution
The FCC process involves combining combustion gas, spent catalyst, and regenerated catalyst in a mixing zone below the regenerator, with a portion of the regenerated catalyst withdrawn from the top of the dense bed and recirculated, and using a lift gas that comprises a significant portion of the combustion gas to enhance mixing and combustion efficiency, mimicking the operation of a combustor style regenerator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If platinum-based CO combustion promoters are used to burn coke to CO2, then CO emissions are decreased, but NOx emissions increase
Solution Approach 1:
The patent removes the platinum-based CO promoter from the system entirely. Instead of using a catalyst to convert CO to CO2, the process allows CO to combust directly with excess oxygen in the fluidized bed, eliminating the source of NOx generation while still achieving complete CO combustion.
Solution Approach 2:
The patent changes the combustion parameters by allowing higher excess oxygen levels (3-10 mol-%) to be present in the fluidized bed. This parameter change enables complete CO combustion without requiring platinum promoters, as the excess oxygen directly oxidizes CO to CO2 through the fluidized bed combustion process.
2Reliability
If excess oxygen is present in the fluidized bed to ensure complete CO combustion, then combustion completeness is improved, but NOx production increases
Solution Approach 1:
The patent converts the harmful effect of excess oxygen (which normally promotes NOx formation) into a beneficial condition by using it to directly oxidize CO to CO2. The excess oxygen that would normally cause NOx problems is instead utilized to complete CO combustion, and the fluidized bed structure allows this to occur without significant NOx generation.
Solution Approach 2:
The patent replaces the catalytic oxidation mechanism (using platinum promoters) with a direct combustion mechanism. Instead of relying on catalyst surfaces to oxidize CO, the process uses direct gas-phase combustion with excess oxygen in the fluidized bed, substituting a chemical catalyst-based system with a thermal combustion system.
3Stability of the object's composition
If a dense fluidized bed is used with superficial velocity less than 1.2 m/s, then catalyst retention is improved, but mixing efficiency decreases
Solution Approach 1:
The patent introduces dynamic circulation of the fluidized bed catalyst. A portion of the regenerated catalyst is recirculated back to the mixing zone where it mixes with spent catalyst, creating dynamic movement and enhanced mixing. This dynamic approach maintains catalyst retention while significantly improving mixing efficiency compared to static dense beds.
Solution Approach 2:
The patent establishes continuous recirculation of regenerated catalyst back to the mixing zone. This continuous action ensures that catalyst particles are constantly being moved, mixed, and regenerated, maintaining both retention and mixing efficiency throughout the process rather than allowing static conditions to develop.
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 reduces NOx emissions, eliminates the need for platinum-based promoters, and decreases excess oxygen requirements, achieving complete CO combustion and more efficient catalyst regeneration with lower NOx emissions.
Implementation Method 1
combining combustion gas, spent catalyst, and regenerated catalyst in a mixing zone below the regenerator
Implementation Method 2
regenerating the spent catalyst into regenerated catalyst in the dense bed
Implementation Method 3
combustion gas, spent catalyst, and regenerated catalyst in a mixing zone below the regenerator
Implementation Method 4
The spent catalyst is introduced into a fluidized bed at the base of the regenerator
Implementation Method 5
the expansion of the gases that result from the vaporization of the hydrocarbons
Implementation Method 6
contacting the heavy hydrocarbons in a fluidized reaction mixing zone with a catalyst composed of finely divided particulate material
Implementation Method 7
the hydrocarbon feed contacts the catalyst and is cracked into a product stream containing lighter hydrocarbons
Implementation Method 8
Coke accumulates on the catalyst particles as a result of the cracking reaction
Implementation Method 9
Regeneration occurs by complete oxidation of the carbonaceous deposits to carbon oxides and water
Data Source
AI summary
An apparatus and process for regenerating cracking catalyst may include a regenerator, a distributor penetrating the bottom of the regenerator, a spent catalyst conduit, a return standpipe, and a recirculating standpipe, wherein the return standpipe and the recirculating standpipe are connected to the upper half of the regenerator. An apparatus for regenerating cracking catalyst may include a spent catalyst standpipe and a recirculation standpipe positioned on an inner side of the regenerator vessel.