C4 Cracking in FCC Stripper via Hot Catalyst Injection
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Solution Overview
Problem
Conventional Fluid Catalytic Cracking (FCC) units face challenges in maximizing propylene yield from C4 hydrocarbons, as existing methods do not effectively optimize temperature and catalyst activity within the stripper bed to enhance C3 olefin production without altering riser conditions or increasing capacity.
Innovation Solution
Injecting a part of the hot regenerated catalyst directly into the stripper bed through an additional catalyst transfer line to achieve optimal Weight Hourly Space Velocity (WHSV) and temperature, thereby enhancing the crackability of the C4 stream for increased propylene production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional FCC processes are used to crack hydrocarbons, then gasoline and general olefinic products are produced, but propylene yield is insufficient to meet growing demand
Solution Approach 1:
The invention divides the cracking process into two distinct zones: a riser for primary cracking and a stripper bed for secondary cracking of C4 hydrocarbons. This segmentation allows optimized conditions for propylene production in the stripper bed while maintaining the original riser configuration for gasoline production, thus resolving the contradiction between maximizing propylene yield and maintaining product slate flexibility.
Solution Approach 2:
The stripper bed acts as an intermediary zone between the riser and the separation system. It receives C4 hydrocarbons from the riser and selectively cracks them to propylene under optimized conditions, serving as a mediating step that enhances propylene yield without interfering with the primary cracking function in the riser.
2Productivity
If temperature and catalyst activity are optimized in the stripper bed, then C4 crackability to propylene is enhanced, but this requires additional equipment or modification of existing units
Solution Approach 1:
The stripper bed is designed to perform multiple functions: it serves as both a catalyst stripping zone (removing adsorbed hydrocarbons from catalyst) and a secondary reaction zone (cracking C4 to propylene). By injecting hydrocarbon feed directly into the stripper bed and optimizing local conditions, the same equipment achieves dual purposes, enhancing propylene production without adding separate cracking equipment.
Solution Approach 2:
The invention changes local parameters within the stripper bed by injecting hydrocarbon feed and introducing a portion of regenerated catalyst, creating optimal temperature and catalyst activity conditions specifically in the stripper bed. This allows C4 cracking to propylene under optimized conditions while maintaining standard riser conditions for gasoline production, resolving the contradiction between enhanced propylene production and device complexity.
3Productivity
If C4 hydrocarbons are cracked to increase propylene yield, then propylene production increases, but stripping efficiency may be compromised
Solution Approach 1:
The invention performs preliminary cracking of C4 hydrocarbons to propylene in the stripper bed before the final separation stage. By converting C4 to propylene in advance, the subsequent separation system receives a product stream already enriched in propylene, improving overall propylene recovery efficiency without compromising the stripping function.
Solution Approach 2:
The invention changes the chemical composition and temperature parameters within the stripper bed by injecting hydrocarbon feed and hot catalyst, creating conditions favorable for C4 cracking. This parameter modification enables simultaneous achievement of propylene production and effective stripping, as the exothermic cracking reactions provide the heat needed for efficient hydrocarbon desorption from the catalyst.
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 results in a significant improvement in propylene yield, up to 1.2 wt% on fresh feed basis, while maintaining existing riser conditions and improving stripping efficiency, making the process more economically viable by also enhancing ethylene production.
Implementation Method 1
Injecting a part of the hot regenerated catalyst directly into the stripper bed through an additional catalyst transfer line to achieve optimal Weight Hourly Space Velocity (WHSV) and temperature
Implementation Method 2
enhancing the crackability of the C4 stream for increased propylene production
Data Source
AI summary
A process for increasing the yield of C3 olefin in fluidized bed catalytic cracking of hydrocarbon feedstocks is disclosed. C4 fraction produced from the cracking of hydrocarbon feedstock in the primary reaction zone (riser), optionally with external source of C4 stream is fed into the stripper which acts as a secondary reaction zone at an elevated temperature and at an optimum WHSV. The elevated temperature is achieved by injecting a part of the regenerated catalyst from regenerator, which is at a higher temperature, directly into the stripper through a dedicated additional lift line. This raises the activity of catalyst inside the stripper. The direct injection of regenerated catalyst into the stripper, besides producing higher yields of propylene, improves the stripping efficiency leading to enhanced recovery of strippable hydrocarbons.