FCCU Propylene Recovery Using Staged C5-C6 Absorption
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Solution Overview
Problem
Conventional methods for propylene recovery from fluid catalytic cracker units (FCCUs) result in significant propylene losses, particularly in fuel gas, limiting the overall recovery rate to around 94%, with a need to enhance propylene recovery by 2 to 3 wt% compared to existing schemes.
Innovation Solution
A method involving the compression and partial condensation of gas streams from the FCCU, followed by sequential heating, separation, and absorption processes using heat exchangers and absorbers to optimize the recovery of propylene-rich streams, particularly leveraging the affinity of C5 and C6 hydrocarbon streams to absorb propylene at specific temperature ranges, and incorporating a propylene absorber to enhance propylene absorption efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional propylene recovery schemes are used, then the process is simple and easy to operate, but propylene recovery rate is limited to around 94% with considerable loss in fuel gas
Solution Approach 1:
The propylene recovery process is divided into multiple sequential absorption stages: a first absorber using C5-C6 rich liquid stream, followed by a second absorber using cooled gas from the first absorber. This segmentation allows each stage to optimize propylene absorption under specific conditions, achieving 97-98% overall recovery compared to conventional single-stage processes.
Solution Approach 2:
The C5-C6 rich liquid stream is prepared in advance through distillation and cooling processes before being introduced to the first absorber. This preliminary preparation ensures the absorbent is at optimal temperature and composition, maximizing propylene absorption efficiency from the outset of the recovery process.
2Productivity
If temperature of C5 and C6 hydrocarbon stream is lowered to enhance propylene absorption, then absorption efficiency increases, but energy consumption increases
Solution Approach 1:
The process optimizes absorption efficiency by controlling the temperature of the C5-C6 liquid stream within a specific range (20-40°C) and the temperature of the gas stream (below 40°C). These parameter changes maximize propylene solubility in the liquid phase while managing energy requirements through heat integration with other process streams.
Solution Approach 2:
The gas stream is cooled between absorption stages, creating periodic temperature variations that enhance propylene absorption in the second absorber. This periodic cooling action allows the system to achieve higher overall recovery while managing thermal energy requirements through staged heat exchange.
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
The method achieves an improved propylene recovery rate of 2 to 3 wt% compared to conventional methods, effectively increasing the overall propylene recovery from FCCU streams by optimizing the absorption processes and temperature conditions.
Implementation Method 1
the stream rich in C5 and C6 hydrocarbons and poor in C7+ hydrocarbons has a good affinity to absorb propylene from light off gases
Implementation Method 2
compressing and partly condensing the gas stream from the main fractionator column overhead receiver of the FCCU
Implementation Method 3
introducing the liquid recovered from the first heat exchanger into a stabilizer column
Data Source
Figure 1
AI summary
The present invention relates to a method for treating a cracked stream stemming from a fluid catalytic cracker unit (FCCU) in order to improve propylene recovery. The present invention also relates to the corresponding installation to implement the method.