Compressed Reflux in Fractionation Towers for Higher NGL Recovery
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Solution Overview
Problem
Conventional cryogenic expansion processes for natural gas liquids recovery suffer from significant losses of C2, C3, and C4+ components due to incomplete rectification, leading to inefficiencies and increased energy requirements.
Innovation Solution
The process incorporates a side draw of vapors from the lower tower combined with a portion of the column overhead vapor, which is compressed to provide reflux for the upper rectification section, enhancing absorption of valuable hydrocarbons and reducing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional cryogenic expansion processes are used for natural gas liquids recovery, then the process provides simplicity and operating flexibility, but significant losses of C2, C3, and C4+ components occur due to incomplete rectification
Solution Approach 1:
The rectification section is divided into two parts: an upper section using the new compressed reflux method and a lower conventional section. This segmentation allows the upper section to provide enhanced rectification for recovering valuable C2, C3, and C4+ components while the lower section maintains conventional operation, thus reducing component losses without requiring complete redesign of the entire process
Solution Approach 2:
The invention changes the parameters of the reflux stream by compressing it to a higher pressure before returning it to the upper rectification section. This parameter change (pressure increase) allows the reflux to provide better cooling and absorption in the upper section, enhancing the rectification efficiency and reducing hydrocarbon losses while maintaining process simplicity
2Ease of operation
If conventional cryogenic expansion processes are used, then ease of operation is maintained, but energy requirements increase due to incomplete rectification and component losses
Solution Approach 1:
The reflux compressor is driven by the expansion machine, creating a self-service arrangement where the expansion process itself provides the power needed for compression. This internal energy recovery reduces the need for external power sources and decreases overall energy requirements while maintaining operating flexibility
Solution Approach 2:
The compressed reflux stream is fed back to the upper rectification section, creating a feedback loop that continuously improves rectification efficiency. This feedback mechanism ensures that valuable components are consistently recovered and returned to the process, reducing energy waste from component losses while maintaining ease of operation
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 achieves C2 recovery exceeding 84%, C3 and C4+ recoveries above 99%, and nearly 100% separation of methane from heavier components at lower energy requirements, while maintaining recovery levels.
Implementation Method 1
A portion of distillation vapor stream withdrawn from the side of the column is compressed to provide reflux for the upper rectification section
Implementation Method 2
The resulting compressed reflux stream is condensed
Implementation Method 3
enhancing absorption of valuable hydrocarbons
Implementation Method 4
the separation of a gas containing hydrocarbons
Data Source
AI summary
A process and an apparatus are disclosed for the recovery of ethane, ethylene, propane, propylene, and heavier hydrocarbon components from a hydrocarbon gas stream. The stream is cooled and divided into first and second streams. The first stream is further cooled to condense substantially all of it and divided into first and second portions. The first and second portions are expanded to the fractionation tower pressure and supplied to the fractionation tower at upper mid-column feed positions, with the expanded second portion being heated before it enters the tower. The second stream is expanded to the tower pressure and supplied to the column at a mid-column feed position. A distillation vapor stream is withdrawn from the column above the feed point of the second stream, combined with a portion of the tower overhead vapor stream, compressed to higher pressure, and directed into heat exchange relation with the remaining tower overhead vapor stream and the expanded second portion to cool the compressed combined vapor stream and condense at least a part of it, forming a condensed stream. At least a portion of the condensed stream is expanded to the tower pressure and directed to the fractionation tower as its top feed. The quantities and temperatures of the feeds to the fractionation tower are effective to maintain the overhead temperature of the fractionation tower at a temperature whereby the major portion of the desired components is recovered.