Hot Water Reboiling for FCC C3 Propylene Fractionation
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Solution Overview
Problem
The separation of propane and propylene by fractionation is costly due to high energy expenditure, particularly in high-pressure processes where the reboiling of the propane/propylene fractionation column requires significant energy and involves the use of process fluids with temperatures greater than 200°C, limiting thermal optimization and increasing the need for low-pressure steam or hot water reboiling.
Innovation Solution
A hot water circuit is used to reboil the propane/propylene separation column, where the water is heated by process fluids from units upstream and downstream of the FCC unit, including overhead vapours from the mild hydrocracking unit, effluent from the HDS reactor, and other high-temperature streams, allowing for two-level reboiling without the need for low-pressure steam and optimizing thermal approaches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-pressure fractionation is used with cooling water condensation, then the separation of propane and propylene can be achieved, but the energy expenditure is very high
Solution Approach 1:
The patent changes the pressure parameter from high-pressure (20-25 bar) to low-pressure (10-15 bar or less) fractionation. This parameter change allows the use of a heat pump system for reboiling instead of high-energy cooling water condensation, significantly reducing energy expenditure while maintaining propylene purity above 99.5%
Solution Approach 2:
The patent utilizes phase transition by employing a heat pump system that recompresses overhead vapors to reboil the column. This phase transition approach (vapour compression and condensation) provides a more energy-efficient reboiling method compared to traditional high-pressure cooling condensation, reducing the energy required for the separation process
2Use of energy by stationary object
If process fluids with temperature greater than 200°C are used for reboiling, then the reboiling function is achieved, but thermal optimization is limited and the temperature margin at the top of the fractionation column is reduced
Solution Approach 1:
The patent applies local quality by using different temperature levels for different parts of the reboiling process. Instead of using single high-temperature fluids (>200°C) for the entire reboiling duty, the system employs multiple process fluids at different temperature levels (e.g., 120-180°C from debutanizer, 80-120°C from circulating reflux) matched to specific reboiler locations, optimizing thermal approaches and maintaining adequate temperature margins at the column top
Solution Approach 2:
The reboiling function is segmented into multiple heat exchange stages using different process fluids at different temperature levels. The patent divides the reboiling duty between various heat exchangers that utilize process fluids from different sources (debutanizer overhead, circulating reflux, etc.), each operating at appropriate temperature margins to avoid excessive temperatures at the column top while still achieving the required reboiling effect
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 energy costs by utilizing higher-temperature process fluids to heat the water circuit, minimizing the area of exchangers and eliminating the need for low-pressure steam, thereby enhancing thermal efficiency and reducing the cost of the hot water circuit while maintaining high propylene purity.
Implementation Method 1
water at approximately 65° C. is heated to a temperature of approximately 91° C. by means of process fluids from the FCC unit
Implementation Method 2
water at approximately 91° C., will reboil the propane/propylene fractionation column
Implementation Method 3
The separation of propane and propylene by fractionation can typically be carried out
Data Source
AI summary
The present invention describes a process for heating the reboiler of the propane/propylene separation column situated downstream of an FCC unit and fed with the C3 cut from said FCC unit, a process consisting of heating the water in a hot water circuit by means of one or more process fluids originating from units placed upstream and/or downstream of the FCC unit and called hot fluids, one of these fluids being constituted by the overhead vapours from the fractionation column connected to the mild hydrocracking unit.