Dual-Riser FCC Process for C3/C4 Olefin and Aromatic Production
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Solution Overview
Problem
Current fluid catalytic cracking (FCC) units face challenges in maximizing the production of aromatics from light hydrocarbon feedstocks, particularly LPG, due to insufficient coke production, which leads to heat balance issues and reduced yields of valuable petrochemicals like ethylene and propylene.
Innovation Solution
A dual-riser FCC system using a gallium-promoted alumina catalyst is employed, where a first riser processes a heavy feedstock and a second riser processes a light hydrocarbon feed, such as LPG, under different conditions to enhance olefin and aromatic production, with the gallium-promoted catalyst facilitating higher temperatures and longer residence times in the second riser to increase aromatic yields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If light hydrocarbon feedstocks (C3/C4) are used in conventional FCC units, then production of valuable petrochemicals (ethylene and propylene) is increased, but insufficient coke production leads to heat balance issues
Solution Approach 1:
The process divides the cracking operation into two separate risers: a first riser for heavy feedstock cracking that generates coke and heat, and a second riser for light hydrocarbon cracking that produces petrochemicals. This segmentation allows each riser to be optimized for its specific function, with the first riser serving as a heat source for the second riser, thereby resolving the heat balance issue while maintaining high petrochemical production.
2Productivity
If heavy feedstock is cracked at high severity to maximize petrochemical yields, then more coke is produced, but this creates excessive heat that leads to system heat imbalance
Solution Approach 1:
The first riser system is designed to self-regulate its coke production and heat generation to match the heat requirements of the second riser. By optimizing the operating conditions of the first riser, the system automatically provides the necessary heat for light hydrocarbon cracking without requiring external heat input or causing heat imbalance, making the overall system self-balancing.
3Device complexity
If a single riser system is used for both heavy and light feeds, then device complexity is reduced, but manufacturing precision and product selectivity cannot be optimized for both feed types
Solution Approach 1:
The dual riser configuration separates the cracking functions into distinct units, each optimized for specific feed types and product distributions. The first riser is optimized for heavy feedstock conversion with appropriate catalyst and temperature conditions, while the second riser is optimized for light hydrocarbon cracking to maximize petrochemical yields. This segmentation enables precise control over product selectivity for each feed type independently.
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 effectively increases aromatic yields and improves heat balance by utilizing the gallium-promoted catalyst to optimize cracking conditions, leading to higher production of BTX (benzene, toluene, and xylene) and overall petrochemical output from light hydrocarbon feeds.
Implementation Method 1
a gallium-promoted alumina catalyst is employed, where a first riser processes a heavy feedstock and a second riser processes a light hydrocarbon feed
Implementation Method 2
The cracking reaction is endothermic, meaning that heat must be supplied to the reactor process to heat the feedstock and maintain reaction temperature
Implementation Method 3
The coke is deposited on the catalyst and ultimately burned with an oxygen source such as air in a regenerator. Burning of the coke is an exothermic process that can supply the heat needed for the cracking reaction
Data Source
AI summary
A dual riser FCC process for converting C3/C4-containing feedstocks to aromatics. First and second hydrocarbon feeds (5, 6) are supplied to the respective first and second risers (2, 4) in a dual-riser FCC unit with a gallium enriched catalyst to make an effluent rich in ethylene, propylene and aromatics. The first riser (2) is operated at less severe conditions than the second riser (4) and can receive a relatively heavy feed such as gas oil. The feed to the second riser (4) includes propane, for example LPG, propane recycle from the C3 splitter (72), etc. The FCC catalyst can include gallium to promote aromatics formation.